Options¶

-A account

Executes an account command (see below) for account after the startup files have been read.

-a file

Attach the given file to the message. The same filename conventions as described in the section COMMANDS apply: shell word expansion is restricted to the tilde ‘~’ and variables. Shall file not be accessible but contain a ‘=’ character, then anything after the ‘=’ is assumed to specify the input character set and anything before ‘=’ the filename: this is the only option to specify the input character set (and don't perform any character set conversion) for text attachments from the command line, not using the ~@ tilde escape command.

-B

Make standard input and standard output line-buffered.

-b address

Send blind carbon copies to the given list of addresses. Sending mail below goes into more detail on that.

-c address

Send carbon copies to the given list of addresses.

-D

[Option] Set the disconnected variable.

-d

Set the debug variable, which enables debug messages and disables message delivery.

-E

Set the skipemptybody variable and thus discard messages with an empty message part body. This is useful for sending messages from scripts.

-e

Just check if mail is present in the system mailbox. If yes, return an exit status of zero, a non-zero value otherwise.

-F

Save the message to send in a file named after the local part of the first recipient's address (instead of in record).

-f [file]

Read in the contents of the user's MBOX (or the specified file) for processing; when S-nail is quit, it writes undeleted messages back to this file (but be aware of the hold option). Some special conventions are recognized for the string file which are documented for the file command below. Note that file is not a direct argument to the flag -f, but is instead taken from the command line after option processing has been completed. In order to use a file that starts with a hyphen, prefix it with a (relative) path, as in ‘./-hyphenbox.mbox’.

-H

Print a header summary of all messages and exit. A configurable summary view is available via the -L option.

-h

Print a short usage summary. Because of widespread use a --help argument will have the same effect.

-i

Set the ignore variable to ignore tty interrupt signals.

-L spec-list

Print a header summary of only those messages that match the given spec-list, then exit. See the section Specifying messages for the format of spec-list. If the -H option has been given in addition no header summary is produced, but S-nail will instead indicate via its exit status whether spec-list matched any messages (‘0’) or not (‘1’); note that any verbose output is suppressed in this mode and must instead be enabled explicitly (e.g., by using the option -v).

-N

Unset the header variable and thus inhibit initial display of message headers when reading mail or editing a mail folder.

-n

Inhibits reading s-nail.rc upon startup. This option should be activated for S-nail scripts that are invoked on more than one machine, because the contents of that file may differ between them. (The same behaviour can be achieved by setting the NAIL_NO_SYSTEM_RC environment variable.)

-q file

Start the message with the contents of the specified file. May be given in send mode only.

-R

Any folder opened will be in read-only mode.

-r address

If address is a valid address then it specifies the envelope sender address to be passed to the MTA as ‘-f address’ when a message is send. Shall address include a user name, comments etc., then the components will be separated and the name part will be passed to the MTA individually via ‘-F name’. The given address will also be assigned to the from variable, just as if additionally ‘-Sfrom=address’ had been specified (therefore affecting SMTP data transfer, too).

If instead an empty string is passed as address then the content of the variable from will be evaluated and used for this purpose whenever the MTA is contacted. Note that S-nail by default, without -r that is, neither passes ‘-f’ nor ‘-F’ flags to the MTA by itself.

-S variable[=value]

Sets the internal option variable and, in case of a value option, assigns value to it. Even though options set via -S may be overwritten from within resource files, the command line setting will be reestablished after all resource files have been loaded.

-s subject

Specify the subject of the to-be-sent message.

-t

The message to be sent is expected to contain a message header with ‘To:’, ‘Cc:’, or ‘Bcc:’ fields giving its recipients, which will be added to those given on the command line. If a message subject is specified via ‘Subject:’ then it'll be used in favour of one given on the command line.

Also understood are ‘Reply-To:’ (possibly overriding replyto), ‘Sender:’ (p. o. sender), ‘Organization:’ (p. o. ORGANIZATION). Note you can also specify ‘From:’, possibly overriding from and the envelope address possibly specified with the option -r!

The following, which are normally created automatically based upon the message context, can also be specified: ‘Message-ID:’, ‘In-Reply-To:’, ‘References:’ and ‘Mail-Followup-To:’ (special address massage will however still occur for the latter).

-u user

Read the system mailbox of user (appropriate privileges presumed), and “assume to be” user in some aspects, e.g. in respect to file–expansions of ‘%’ etc.; also see USER.

-V

Print S-nail's version and exit.

-v

Setting the verbose option causes some verbosity (like printing of certificate chains). Using it twice increases the level of verbosity.

-X cmd

Add the given cmd to the list of commands to be executed before normal operation starts. Correlates with -# and batch-exit-on-error; the only possibility to execute commands in non-interactive mode when reading startup files is actively prohibited.

-~

Enable TILDE ESCAPES even if not in interactive mode.

-#

This sets several options to prepare S-nail for working in (most likely non-interactive) batch mode: dot, emptystart, noheader, quiet, sendwait, as well as MBOX and folder (both to /dev/null). It also enables processing of TILDE ESCAPES. E.g., the following should send an email message to “bob”:

$ LC_ALL=C printf 'm bob\n~s ubject\nText\n.\nx\n' | \
  LC_ALL=C MAILRC=/dev/null s-nail -n -# -Snosave
    

-.

This flag forces termination of option processing in order to prevent “option injection” (attacks). It also forcefully puts S-nail into send mode, see Sending mail.

In the above list of supported command line options, -D, -d, -E, -i, -N and -v are implemented by means of setting the respective option, as via -S. [mta-option ...] arguments that are given at the end of the command line after a ‘--’ separator will be passed through to the mail-transfer-agent (MTA) and persist for an entire (interactive) session – if the setting of expandargv allows their recognition; MTA arguments can also be specified in the variable sendmail-arguments; find MTA interaction described in more detail in the documentation of sendmail. MTA arguments are ignored when mail is send via SMTP data transfer.

A starter¶

S-nail is thus the user side of the Unix mail system, whereas the system side (mail-transfer-agent, MTA) was traditionally taken by sendmail(8); today postfix(1) or exim(8) are often used for this purpose instead. If the [Option]al SMTP feature has been built into S-nail then the system side is not a mandatory precondition for mail delivery.

Because S-nail strives for compliance with POSIX mailx(1) it is likely that some configuration settings have to be adjusted before using it is a smooth experience. The default global s-nail.rc file already bends those standard settings a bit towards more user friendliness and safety, e.g., it sets the hold and keepsave options in order to suppress the automatic moving of messages to MBOX that would otherwise occur (see Message states) and keep to not remove empty files in order not to mangle file permissions when files eventually get recreated. It does not set the folder option so that by default file grouping (via the ‘+’ prefix as documented also for file) is not enabled. The section EXAMPLES contains some further suggestions.

Sending mail¶

$ s-nail -s Subject -a attachm.ent bill@host1 'Bob <bob@host2>'
# But... try it in an isolated dry-run mode first
$ LC_ALL=C MAILRC=/dev/null \
  s-nail -n -d -vv -Sfrom="me <he@re>" \
    -s Subject -. "(Lovely) Bob <bob@host2>"

The user is then expected to type in the message contents. In this compose mode S-nail treats lines beginning with the character ‘~’ special – these are so-called TILDE ESCAPES which can be used to read in files, process shell commands, add and edit attachments and more; e.g., the tilde escape ‘~e’ will start the text editor to revise the message in it's current state, ‘~h’ allows editing of the message recipients and ‘~?’ gives an overview of available tilde escapes. Typing control-D ‘^D’ at the beginning of an empty line leaves compose mode and causes the message to be send, whereas typing control-C ‘^C’ twice will abort the current letter (saving its contents in the file denoted by DEAD unless nosave is set.)

A number of options can be used to alter default behavior; e.g., setting (also via -S) editalong will automatically startup a text editor when compose mode is entered, askcc will cause the user to be prompted actively for carbon-copy recipients and the dot option will allow leaving compose mode by writing a line consisting solely of a dot (‘.’).

Very important, though, is to define which Character sets may be used when sending messages, usually by setting the option sendcharsets accordingly, having read the section The mime.types files to understand how the MIME-type of outgoing attachments is classified and the knowledge that messages are sent asynchronously unless sendwait is set: only with it MTA delivery errors will be recognizable.

Setting from is often necessary (e.g., in conjunction with smtp) or desirable, you may want to do some dry-run tests before you go. Saving a copy of the sent messages in a record may also be desirable – as for most mailbox file targets some special conventions are recognized, see the file command for more on that. The section On URL syntax and credential lookup will spread some light on the ‘USER@HOST’ variable chains as well as on using URLs for accessing protocol-specific resources, like smtp, and EXAMPLES contains an example configuration for sending messages via some of the well-known public mail providers; note it also gives a compact overview on how to setup a secure SSL/TLS environment.

Message recipients (as specified on the command line or defined in ‘To:’, ‘Cc:’ or ‘Bcc:’) may not only be email addressees but can also be names of mailboxes and even complete shell command pipe specifications. Proper quoting may be necessary, e.g., to embed whitespace characters. (Recall that S-nail deals with mail standards, therefore those define the rules with which content is interpreted.) If the variable expandaddr is not set then only network addresses (see mailaddr(7) for a description of mail addresses) and plain user names (including MTA aliases) may be used, other types will be filtered out, giving a warning message.

If the variable expandaddr is set then extended recipient addresses will optionally be accepted: Any name which starts with a vertical bar ‘|’ character specifies a command pipe – the command string following the ‘|’ is executed and the message is sent to its standard input; Likewise, any name that starts with the character slash ‘/’ or the character sequence dot slash ‘./’ is treated as a file, regardless of the remaining content. Any other name which contains an at sign ‘@’ character is treated as a network address; Any other name which starts with a plus sign ‘+’ character specifies a mailbox name; Any other name which contains a slash ‘/’ character but no exclamation mark ‘!’ or percent sign ‘%’ character before also specifies a mailbox name; What remains is treated as a network address.

$ echo bla | s-nail -Sexpandaddr -s test ./mbox.mbox
$ echo bla | s-nail -Sexpandaddr -s test '|cat >> ./mbox.mbox'
$ echo safe | LC_ALL=C MAILRC=/dev/null \
    s-nail -n -Sv15-compat -Ssendwait -Snosave \
      -Sexpandaddr=fail,-all,+addr -s test \
      -. bob@home.net

It is possible to create personal distribution lists via the alias command, so that, for instance, the user can send mail to ‘cohorts’ and have it go to a group of people:

Please note that this mechanism has nothing in common with the system wide aliases that may be used by the local MTA (mail-transfer-agent), which are subject to the ‘name’ constraint of expandaddr and are often tracked in a file /etc/aliases (and documented in aliases(5) and sendmail(1)). Personal aliases will be expanded by S-nail before the message is sent, and are thus a convenient alternative to specifying each addressee by itself.

To avoid environmental noise scripts should “detach” s-nail from any configuration files and create a script-local environment, either by pointing the MAILRC variable to a custom configuration file, or by using the -S command line option to specify options:

$ env LC_ALL=C MAILRC=/dev/null password=NOTSECRET \
  s-nail -n -Sv15-compat -Ssendwait -Snosave \
    -Sexpandaddr=fail,-all,+addr \
    -S 'smtp=smtps://mylogin@some.host:465' -Ssmtp-auth=login \
    -S 'from=scriptreply@domain' \
    -s 'subject' -a attachment_file \
    -. "Recipient 1 <recipient1@domain>" recipient2@domain \
    < content_file

Reading mail¶

At the prompt the command list will give a listing of all available commands and help will give a summary of some common ones. If the [Option]al documentation strings are available one can type ‘?X’ and see the actual expansion of ‘X’ and what it's purpose is, i.e., commands can be abbreviated (note that POSIX defines some abbreviations, so that the alphabetical order of commands doesn't necessarily relate to the abbreviations; it is possible to define overwrites with the ghost command, however).

Messages are given numbers (starting at 1) which uniquely identify messages; the current message – the “dot” – will either be the first new message, or the first unread message, or the first message of the mailbox; the option showlast will instead cause usage of the last message for this purpose.

Messages can be printed with the print command, or short: ‘p’. By default the current message (“dot”) is printed, but like with most other commands it is possible to give a fancy message specification (see Specifying messages), e.g., ‘p:u’ will display all unread messages, ‘p.’ will print the “dot”, ‘p 1 5’ will print the messages 1 and 5, ‘p 1-5’ will print the messages 1 through 5, and ‘p-’ and ‘p+’ will print the last and the next message, respectively.

In the default setup all header fields of a message will be printed, but this can be changed: either by blacklisting a list of fields via ignore, or by whitelisting only a given list with the retain command, e.g., ‘retain date from to cc subject’. In order to print all header fields of a message regardless of currently active ignore or retain lists, use the command Print. The variable crt controls whether and when S-nail will use the configured PAGER for printing instead of directly writing to the terminal (generally speaking).

Dependent upon the configuration a Command line editor aims at making user experience with the many COMMANDS a bit nicer. When reading the system mailbox or when -f (or file) specified a mailbox explicitly prefixed with the special ‘%:’ modifier then messages which have been read will be moved to the user's MBOX file automatically when the mailbox is left, either by changing the active mailbox or by quitting S-nail (also see Message states).

After examining a message the user can also delete ‘d’ the message, reply ‘r’ to the sender and all recipients or Reply ‘R’ exclusively to the sender. Messages can also be forwarded (shorter alias is fwd). Note that when replying to or forwarding a message recipient addresses will be stripped from comments and names unless the option fullnames is set. Deletion causes S-nail to forget about the message; This is not irreversible, though, one can undelete ‘u’ the message by giving its number, or the S-nail session can be ended by giving the exit ‘x’ command.

To end a mail processing session one may either issue quit ‘q’ to cause a full program exit, which possibly includes automatic moving of read messages to MBOX as well as updating the [Option]al command line editor history file, or use the command exit ‘x’ instead in order to prevent any of these actions.

Viewing HTML mail and MIME attachments¶

To install an external handler program for a specific MIME type set an according pipe-TYPE/SUBTYPE variable. To define a handler for a specific file extension set the respective pipe-EXTENSION variable – these handlers take precedence. The variable mime-counter-evidence can be set to improve dealing with faulty MIME part declarations as are often seen in real-life messages. E.g., to display a HTML message inline (that is, converted to a more fancy plain text representation than the builtin converter is capable to produce) with either of the text-mode browsers lynx(1) or elinks(1), teach S-nail about MathML documents and make it display them as plain text and to open PDF attachments in an external PDF viewer, asynchronously:

if $features !@ HTML-FILTER
  #set pipe-text/html="elinks -force-html -dump 1"
  set pipe-text/html="lynx -stdin -dump -force_html"
  # Display HTML as plain text instead
  #set pipe-text/html=@
endif
mimetype '@ application/mathml+xml mathml'
set pipe-application/pdf="@&set -C;\
    : > \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\"; \
    trap \"rm -f \\\"${TMPDIR}/${NAIL_FILENAME_GENERATED}\\\"\" \
      EXIT INT QUIT PIPE TERM;\
    set +C;\
    cat > \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\"; \
    xpdf \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\""

Note: special care must be taken when using such commands as mail viruses may be distributed by this method: if messages of type ‘application/x-sh’ or files with the extension ‘.sh’ were blindly filtered through the shell, for example, a message sender could easily execute arbitrary code on the system S-nail is running on. For more on MIME, also in respect to sending of messages, see the section The mime.types files and the command mimetype.

Mailing lists¶

[Option]ally mailing lists may also be specified as regular expressions, which allows matching of many addresses with a single expression. However, all fully qualified list addresses are matched via a fast dictionary, whereas expressions are placed in (a) list(s) which is (are) matched sequentially.

set followup-to followup-to-honour=ask-yes reply-to-honour=ask-yes
mlist a1@b1.c1 a2@b2.c2 .*@lists.c3$
mlsubscribe a4@b4.c4 exact@lists.c3

The variable followup-to-honour will ensure that a ‘Mail-Followup-To:’ header is honoured when the message is being replied to (via reply and Lreply) and followup-to controls whether this header is created when sending mails; it will be created automatically for a couple of reasons, too, like when the special “mailing list specific” respond command Lreply is used, when reply is used to respond to a message with its ‘Mail-Followup-To:’ being honoured etc.

A difference in between the handling of known and subscribed lists is that the address of the sender is usually not part of a generated ‘Mail-Followup-To:’ when addressing the latter, whereas it is for the former kind of lists. Usually because there are exceptions: say, if multiple lists are addressed and not all of them are subscribed lists.

For convenience S-nail will, temporarily, automatically add a list address that is presented in the ‘List-To:’ header of a message that is being responded to to the list of known mailing lists. Shall that header have existed S-nail will instead, dependend on the variable reply-to-honour, use an also set ‘Reply-To:’ for this purpose in order to accept a list administrators' wish that is supposed to have been manifested like that (but only if it provides a single address which resides on the same domain as what is stated in ‘List-To:’).

Resource files¶

s-nail.rc

System wide initialization file. Reading of this file can be suppressed, either by using the -n command line option, or by setting the environment variable NAIL_NO_SYSTEM_RC.

~/.mailrc

File giving initial commands. A different file can be chosen by setting the environment variable MAILRC.

NAIL_EXTRA_RC

Can be used to define an optional startup file to be read after ~/.mailrc. This variable is only honoured in certain circumstances (see its documentation for more).

The content of these files is interpreted as follows:

• A lines' leading whitespace is ignored.
• An empty line is ignored.
• If the line (content) starts with the number sign ‘#’ then it is a comment-command – a real command! – and also ignored. This command is the only form of comment that is understood.
• A line can be “continued” on the next line if the newline character is “escaped” by preceding it with the backslash character ‘\’. Note that any leading whitespace of follow lines is removed: If whitespace is desired it must be placed before the backslash. For example:

   # This line is a comment command.  And y\
      es, it is really continued here.
  set debug \
      verbose
      

Character sets¶

However, a user supplied ttycharset value is not overwritten by this detection mechanism: this “feature” must be used if the detection doesn't work properly, and it may be used to adjust the name of the locale character set. E.g., on BSD systems one may use a locale with the character set ISO8859-1, which is not a valid name for this character set; to be on the safe side, one may set ttycharset to the correct name, which is ISO-8859-1.

Note that changing the value doesn't mean much beside that, since several aspects of the real character set are implied by the locale environment of the system, and that stays unaffected by the content of an overwritten ttycharset variable. (This is mostly an issue when interactively using S-nail, though. It is actually possible to send mail in a completely “faked” locale environment.)

If no character set conversion capabilities have been compiled into S-nail (i.e., no iconv(3) library has been found), then ttycharset will be the only supported character set, it is simply assumed that it can be used to exchange 8-bit messages, and the rest of this section does not apply; it may however still be necessary to explicitly set it if automatic detection fails, since in that case it defaults to the mentioned ISO-8859-1.

When reading messages, their text is converted into ttycharset as necessary in order to display them on the users terminal. Unprintable characters and invalid byte sequences are detected and replaced by proper substitution characters (unless the variable print-all-chars was set once S-nail was started). Also see charset-unknown-8bit to deal with another hairy aspect of message interpretation.

When sending messages all their parts and attachments are classified. Whereas no character set conversion is performed on those parts which appear to be binary data, the character set being used must be declared within the MIME header of an outgoing text part if it contains characters that do not conform to the set of characters that are allowed by the email standards. Permissible values for character sets can be declared using the sendcharsets variable, and charset-8bit, which defines a catch-all last-resort fallback character set that is implicitly appended to the list of character-sets in sendcharsets.

When replying to a message and the variable reply-in-same-charset is set then the character set of the message being replied to is tried first. And it is also possible to make S-nail work even more closely related to the current locale setting automatically by using the variable sendcharsets-else-ttycharset, please see there for more information.

All the specified character sets are tried in order unless the conversion of the part or attachment succeeds. If none of the tried (8-bit) character sets is capable to represent the content of the part or attachment, then the message will not be sent and its text will be saved to DEAD. In general, if the message “Cannot convert from a to b” appears, either some characters are not appropriate for the currently selected (terminal) character set, or the needed conversion is not supported by the system. In the first case, it is necessary to set an appropriate LC_CTYPE locale and/or the variable ttycharset.

The best results are usually achieved when S-nail is run in a UTF-8 locale on a UTF-8 capable terminal, in which case the full Unicode spectrum of characters is available. In this setup characters from various countries can be displayed, while it is still possible to use more simple character sets for sending to retain maximum compatibility with older mail clients.

Message states¶

‘new’

Message has neither been viewed nor moved to any other state. Such messages are retained even in the system mailbox.

‘unread’

Message has neither been viewed nor moved to any other state, but the message was present already when the mailbox has been opened last: Such messages are retained even in the system mailbox.

‘read’

The message has been processed by one of the following commands: ~f, ~m, ~F, ~M, copy, mbox, next, pipe, print, Print, top, type, Type, undelete. The delete, dp, and dt commands may also cause the next message to be marked as read, depending on the value of the autoprint variable. Except when the exit command is used, messages that are in the system mailbox or in mailboxes which were opened with the special ‘%:’ prefix and are in ‘read’ state when the mailbox is left will be saved in MBOX unless the option hold it set.

‘deleted’

The message has been processed by one of the following commands: delete, dp, dt. Only undelete can be used to access such messages.

‘preserved’

The message has been processed by a preserve command and it will be retained in its current location.

‘saved’

The message has been processed by one of the following commands: save or write. Unless when the exit command is used, messages that are in the system mailbox or in mailboxes which were opened with the special ‘%:’ prefix and are in ‘saved’ state when the mailbox is left will be deleted; they will be saved in MBOX when the option keepsave is set.

Specifying messages¶

:n

All ‘new’ messages.

:o

All old messages (any not in state ‘read’ or ‘new’).

:u

All ‘unread’ messages.

:d

All ‘deleted’ messages (for the undelete command).

:r

All ‘read’ messages.

:f

All flagged messages.

:a

All answered messages (cf. the markanswered variable).

:t

All messages marked as draft.

:s

[Option] All messages classified as spam.

:S

[Option] All messages with unsure spam classification.

.

The current message, the so-called “dot”.

;

The message that was previously the current message.

,

The parent message of the current message, that is the message with the Message-ID given in the ‘In-Reply-To:’ field or the last entry of the ‘References:’ field of the current message.

-

The next previous undeleted message, or the next previous deleted message for the undelete command. In sorted/threaded mode, the next previous such message in the sorted/threaded order.

+

The next undeleted message, or the next deleted message for the undelete command. In sorted/threaded mode, the next such message in the sorted/threaded order.

^

The first undeleted message, or the first deleted message for the undelete command. In sorted/threaded mode, the first such message in the sorted/threaded order.

$

The last message. In sorted/threaded mode, the last message in the sorted/threaded order.

&x

In threaded mode, selects the message addressed with x, where x is any other message specification, and all messages from the thread that begins at it. Otherwise it is identical to x. If x is omitted, the thread beginning with the current message is selected.

*

All messages.

`

All messages that were included in the message list for the previous command.

/string

All messages that contain string in the subject field (case ignored). See also the searchheaders variable. If string is empty, the string from the previous specification of that type is used again.

[@name-list]@expr

All messages that contain the given case-insensitive search expression; if the [Option]al regular expression (see re_format(7)) support is available expr will be interpreted as one if any of the “magical” regular expression characters is seen. If the optional @name-list part is missing, the search is restricted to the subject field body, but otherwise name-list specifies a comma-separated list of header fields to search, as in

'@to,from,cc@Someone i ought to know'

In order to search for a string that includes a ‘@’ (commercial at) character the name-list is effectively non-optional, but may be given as the empty string. Some special header fields may be abbreviated: ‘f’, ‘t’, ‘c’, ‘b’ and ‘s’ will match ‘From’, ‘To’, ‘Cc’, ‘Bcc’ and ‘Subject’, respectively and case-insensitively. The special names ‘header’ or ‘<’ can be used to search in (all of) the header(s) of the message, and the special names ‘body’ or ‘>’ and ‘text’ or ‘=’ can be used to perform full text searches – whereas the former searches only the body, the latter also searches the message header.

This message specification performs full text comparison, but even with regular expression support it is almost impossible to write a search expression that savely matches only a specific address domain. To request that the content of the header is treated as a list of addresses, and to strip those down to the plain email address which the search expression is to be matched against, prefix the header name (abbreviation) with a tilde ‘~’:

'@~f@@a\.safe\.domain\.match$'

address

A case-insensitive “any substring matches” search against the ‘From:’ header, which will match addresses (too) even if showname is set (and POSIX says “any address as shown in a header summary shall be matchable in this form”); However, if the allnet variable is set, only the local part of the address is evaluated for the comparison, not ignoring case, and the setting of showname is completely ignored. For finer control and match boundaries use the ‘@’ search expression; the [Option]al IMAP-style ‘(from address)’ expression can also be used if substring matches are desired.

[Option] IMAP-style SEARCH expressions may also be used. This addressing mode is available with all types of folders; S-nail will perform the search locally as necessary. Strings must be enclosed by double quotes ‘"’ in their entirety if they contain white space or parentheses; within the quotes, only backslash ‘\’ is recognized as an escape character. All string searches are case-insensitive. When the description indicates that the “envelope” representation of an address field is used, this means that the search string is checked against both a list constructed as

("name" "source" "local-part" "domain-part")

for each address, and the addresses without real names from the respective header field. These search expressions can be nested using parentheses, see below for examples.

(criterion)

All messages that satisfy the given criterion.

(criterion1 criterion2 ... criterionN)

All messages that satisfy all of the given criteria.

(or criterion1 criterion2)

All messages that satisfy either criterion1 or criterion2, or both. To connect more than two criteria using ‘or’ specifications have to be nested using additional parentheses, as with ‘(or a (or b c))’, since ‘(or a b c)’ really means ‘((a or b) and c)’. For a simple ‘or’ operation of independent criteria on the lowest nesting level, it is possible to achieve similar effects by using three separate criteria, as with ‘(a) (b) (c)’.

(not criterion)

All messages that do not satisfy criterion.

(bcc "string")

All messages that contain string in the envelope representation of the ‘Bcc:’ field.

(cc "string")

All messages that contain string in the envelope representation of the ‘Cc:’ field.

(from "string")

All messages that contain string in the envelope representation of the ‘From:’ field.

(subject "string")

All messages that contain string in the ‘Subject:’ field.

(to "string")

All messages that contain string in the envelope representation of the ‘To:’ field.

(header name "string")

All messages that contain string in the specified ‘Name:’ field.

(body "string")

All messages that contain string in their body.

(text "string")

All messages that contain string in their header or body.

(larger size)

All messages that are larger than size (in bytes).

(smaller size)

All messages that are smaller than size (in bytes).

(before date)

All messages that were received before date, which must be in the form ‘d[d]-mon-yyyy’, where ‘d’ denotes the day of the month as one or two digits, ‘mon’ is the name of the month – one of ‘Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec’, and ‘yyyy’ is the year as four digits, e.g., ‘28-Dec-2012’.

(on date)

All messages that were received on the specified date.

(since date)

All messages that were received since the specified date.

(sentbefore date)

All messages that were sent on the specified date.

(senton date)

All messages that were sent on the specified date.

(sentsince date)

All messages that were sent since the specified date.

()

The same criterion as for the previous search. This specification cannot be used as part of another criterion. If the previous command line contained more than one independent criterion then the last of those criteria is used.

On URL syntax and credential lookup¶

If ‘USER’ and ‘PASSWORD’ are specified as part of an URL they must be given in URL percent encoded (RFC 3986) form – the command urlcodec can be used to perform the encoding and show the encoded value. (This doesn't really conform to any standard, but for one it isn't used for any data exchange over the internet, and second it's easier for users to simply call urlcodec on a string and use that instead of having to deal with several different standards.) On the other hand, values given in variable names are expected not to be URL percent encoded.

Many variable options of S-nail exist in multiple versions, called variable chains for the rest of this document: the plain ‘variable’ as well as ‘variable-HOST’ and ‘variable-USER@HOST’. Here ‘HOST’ indeed means ‘server:port’ if a ‘port’ had been specified in the respective URL, otherwise it refers to the plain ‘server’. Also, ‘USER’ isn't truly the ‘USER’ that had been found when doing the user chain lookup as is described below, i.e., this ‘USER’ will never be in URL percent encoded form, whether it came from an URL or not.

For example, whether an hypothetical URL ‘smtp://hey%3Ayou@our.house’ had been given that includes a user, or whether the URL was ‘smtp://our.house’ and the user had been found differently, to lookup the variable chain smtp-use-starttls S-nail first looks for whether ‘smtp-use-starttls-hey:you@our.house’ is defined, then whether ‘smtp-use-starttls-our.house’ exists before finally ending up looking at the plain variable itself.

S-nail obeys the following logic scheme when dealing with the necessary credential informations of an account:

• If no ‘USER’ has been given in the URL the variables user-HOST and user are looked up; if no such variable(s) can be found then S-nail will, when enforced by the [Option]al variables netrc-lookup-HOST or netrc-lookup, search the users .netrc file for a ‘HOST’ specific entry which provides a ‘login’ name: this lookup will only succeed if unambiguous (one possible matching entry for ‘HOST’).

  If there is still no ‘USER’ then S-nail will fall back to the user who is supposed to run S-nail: either the name that has been given with the -u command line option (or, equivalently, but with less precedence, the environment variable USER), or the “current” user. The identity of this user has been fixated during S-nail startup and is known to be a valid user on the current host.

• Authentication: unless otherwise noted this will lookup the PROTOCOL-auth-USER@HOST, PROTOCOL-auth-HOST, PROTOCOL-auth variable chain, falling back to a protocol-specific default should this have no success.
• If no ‘PASSWORD’ has been given in the URL – it should be noted once that specifying the password in the URL is only syntactic sugar for the user, it'll never be part of an URL that S-nail uses itself –, then if the ‘USER’ has been found through the [Option]al .netrc file lookup then that may have already provided the password, too. Otherwise the variable chain password-USER@HOST, password-HOST, password is looked up.

  [Option] Then if any of the variables of the chain agent-shell-lookup-USER@HOST, agent-shell-lookup-HOST, agent-shell-lookup is set the shell command specified therein is run and the output (less newline characters) will be used as the password. It is perfectly valid for such an agent to simply not return any data, in which case the password lookup is continued somewhere else; Any command failure is treated as a hard error, however.

  The next variable chain that is inspected is the [Option]al netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup, but this time looking only for the password (multiple user accounts for a single machine may exist as well as a fallback entry without user but with a password).

  If at that point there is still no password available, but the (protocols') chosen authentication type requires a password, then in interactive mode the user will be prompted on the terminal.

Note: S/MIME verification works relative to the values found in the ‘From:’ (or ‘Sender:’) header field(s), which means that the values of smime-sign, smime-sign-cert, smime-sign-include-certs and smime-sign-message-digest will not be looked up using the ‘USER’ and ‘HOST’ chains from above but instead use the corresponding values from the message that is being worked on. In unusual cases multiple and different ‘USER’ and ‘HOST’ combinations may therefore be involved – on the other hand those unusual cases become possible. The usual case is as short as:

The section EXAMPLES contains complete example configurations.

Command line editor¶

Regardless of the actually used command line editor history entries will be created for lines entered in command mode only, and creation of such an entry can be forcefully suppressed by starting the line with a space character. Note that history handling is by itself an optional feature and may therefore not be available. For more information see the documentation of the options emptystart, history-gabby, history-gabby-persist, line-editor-disable, NAIL_HISTFILE and NAIL_HISTSIZE.

The builtin S-nail command line editor supports the following operations; the notation ‘^-character’ stands for the combination of the “Control” key plus the mentioned character, e.g., ‘^A’ means “hold down control key and press the A key”:

‘^A’

Go to the start of the line.

‘^B’

Move the cursor backward one character.

‘^D’

Forward delete the character under the cursor; quits S-nail if used on the empty line unless the ignoreeof option is set.

‘^E’

Go to the end of the line.

‘^F’

Move the cursor forward one character.

‘^G’

Cancel current operation, full reset. If there is an active history search or tabulator expansion then this command will first reset that, reverting to the former line content; thus a second reset is needed for a full reset in this case. In all cases S-nail will reset a possibly used multibyte character input state machine.

‘^H’

The same as “backspace”: backward delete one character.

‘^I’

[Option] The same as “horizontal tabulator”: try to expand the word before the cursor. (Note this is not “tabulator-completion” as is known from the sh(1) but really means the usual S-nail expansion, as documented for file, yet it involves shell expansion as a last step, too.)

‘^J’

The same as “ENTER”: complete this line of input.

‘^K’

Delete all characters from the cursor to the end of the line.

‘^L’

Repaint the line.

‘^N’

[Option] Go to the next history entry.

‘^O’

Execute the command dp.

‘^P’

[Option] Go to the previous history entry.

‘^R’

[Option] Complete the current line from (the remaining older) history entries.

‘^U’

The same as ‘^A’ followed by ‘^K’.

‘^W’

Delete the characters from the one preceding the cursor to the preceding word boundary.

‘^X’

Move the cursor forward one word boundary.

‘^Y’

Move the cursor backward one word boundary.

If problems with commands that are based upon rightwise movement are encountered, adjustments of the option line-editor-cursor-right may solve the problem, as documented for it.

If the terminal produces key sequences which are compatible with xterm(1) then the left and right cursor keys will map to ‘^B’ and ‘^F’, respectively, the up and down cursor keys will map to ‘^P’ and ‘^N’, and the Home/End/PgUp/PgDown keys will call the z command with the respective arguments ‘0’, ‘$’, ‘-’ and ‘+’ (i.e., perform scrolling through the header summary list).

Coloured message display¶

On top of that the binary option colour-pager defines whether these colour sequences are also generated when the output of a command needs to go through the PAGER (also see crt) – this is not enabled by default because different pager programs need different command line switches or other configuration in order to support those colour sequences, please see the option for more details.

To forcefully disable all colour support, set colour-disable.

Colours can be configured through font attributes (‘ft=’ – ‘bold’, ‘invers’ and ‘underline’), foreground (‘fg=’) and background (‘bg=’) colours (‘black’, ‘blue’, ‘green’, ‘red’, ‘brown’, ‘magenta’, ‘cyan’ and ‘white’). Multiple specifications can be joined in a comma separated list, as in

Options to be set are colour-msginfo, colour-partinfo, colour-from_, colour-header and colour-uheader, as well as colour-user-headers, which is a list of headers to be colourized via colour-uheader instead of the default colour-header.

Initial Settings¶

Notes: S-nail doesn't support the noonehop variable – use command line options or sendmail-arguments to pass options through to a MTA. And the default global s-nail.rc file (which is loaded unless the -n command line flag has been used or the NAIL_NO_SYSTEM_RC environment variable is set) bends those initial settings a bit, e.g., it sets the options hold, keepsave and keep, to name a few, calls retain etc., and should thus be taken into account.

Binary options¶

add-file-recipients

When file or pipe recipients have been specified, mention them in the corresponding address fields of the message instead of silently stripping them from their recipient list. By default such addressees are not mentioned.

allnet

Causes only the local part to be evaluated when comparing addresses.

append

Causes messages saved in MBOX to be appended to the end rather than prepended. This should always be set.

ask or asksub

Causes S-nail to prompt for the subject of each message sent. If the user responds with simply a newline, no subject field will be sent.

askatend

Causes the prompts for ‘Cc:’ and ‘Bcc:’ lists to appear after the message has been edited.

askattach

If set, S-nail asks for files to attach at the end of each message, shall the list be found empty at that time. An empty line finalizes the list.

askcc

Causes the user to be prompted for carbon copy recipients (at the end of each message if askatend or bsdcompat are set) shall the list be found empty (at that time). An empty line finalizes the list.

askbcc

Causes the user to be prompted for blind carbon copy recipients (at the end of each message if askatend or bsdcompat are set) shall the list be found empty (at that time). An empty line finalizes the list.

asksign

[Option] Causes the user to be prompted if the message is to be signed at the end of each message. The smime-sign variable is ignored when this variable is set.

autocollapse

Causes threads to be collapsed automatically when threaded mode is entered (see the collapse command).

autoprint

Causes the delete command to behave like ‘dp -’; thus, after deleting a message the next one will be typed automatically.

autothread

[Obsolete] Causes threaded mode (see the thread command) to be entered automatically when a folder is opened. The same as ‘autosort=thread’.

bang

Enables the substitution of ‘!’ by the contents of the last command line in shell escapes.

batch-exit-on-error

If the batch mode has been enabled via the -# command line option, then this variable will be consulted whenever S-nail completes one operation (returns to the command prompt); if it is set then S-nail will terminate if the last operation generated an error.

bsdannounce

Causes automatic display of a header summary after executing a file command.

bsdcompat

Sets some cosmetical features to traditional BSD style; has the same affect as setting askatend and all other variables prefixed with ‘bsd’; it also changes the meaning of the S-nail specific ‘\&’ prompt escape sequence.

bsdflags

Changes the letters printed in the first column of a header summary to traditional BSD style.

bsdheadline

Changes the display of columns in a header summary to traditional BSD style.

bsdmsgs

Changes some informational messages to traditional BSD style.

bsdorder

Causes the ‘Subject:’ field to appear immediately after the ‘To:’ field in message headers and with the ~h TILDE ESCAPES.

bsdset

Changes the output format of the set command to traditional BSD style.

colour-disable

[Option] Forcefully disable usage of colours. Also see the section Coloured message display.

colour-pager

[Option] Whether colour shall be used for output that is paged through PAGER. Note that pagers may need special flags, e.g., less(1) requires the option -R and lv(1) the option -c in order to support colours; therefore S-nail will inspect the variable PAGER – if that starts with the string “less” a non-existing environment variable LESS will be set to ‘FRSXi’, likewise for “lv” LV will optionally be set to “-c”. Also see the section Coloured message display for more on this.

debug

Prints debugging messages and disables the actual delivery of messages. Also implies norecord and nosave.

disconnected

[Option] When an IMAP mailbox is selected and this variable is set, no connection to the server is initiated. Instead, data is obtained from the local cache (see imap-cache). Mailboxes that are not present in the cache and messages that have not yet entirely been fetched from the server are not available; to fetch all messages in a mailbox at once, the command `copy * /dev/null' can be used while still in connected mode. Changes that are made to IMAP mailboxes in disconnected mode are queued and committed later when a connection to that server is made. This procedure is not completely reliable since it cannot be guaranteed that the IMAP unique identifiers (UIDs) on the server still match the ones in the cache at that time. Data is saved to DEAD when this problem occurs.

disconnected-USER@HOST

The specified account is handled as described for the disconnected variable above, but other accounts are not affected.

disposition-notification-send

[Option] Emit a ‘Disposition-Notification-To:’ header (RFC 3798) with the message. This requires a set from variable.

dot

When dot is set, a dot ‘.’ on a line by itself during message input from a terminal shall be treated as end-of-message (in addition to the normal end-of-file condition). If ignoreeof is set nodot is ignored and using a dot is the only method to terminate input mode.

dotlock-ignore-error

[Option] Synchronization of mailboxes which S-nail treats as system mailboxes (see the command file) will be protected with so-called dotlock files—the traditional mail spool file locking method—in addition to system file locking. Because S-nail ships with a privilege-separated dotlock creation program that should always be able to create such a dotlock file there is no good reason to ignore dotlock file creation errors, and thus these are fatal unless this variable is set.

editalong

If this variable is set then the editor is started automatically when a message is composed in interactive mode, as if the ~e TILDE ESCAPES had been specified. The editheaders variable is implied for this automatically spawned editor session.

editheaders

When a message is edited while being composed, its header is included in the editable text. The ‘To:’, ‘Cc:’, ‘Bcc:’, ‘Subject:’, ‘From:’, ‘Reply-To:’, ‘Sender:’, and ‘Organization:’ fields are accepted within the header, other fields are ignored.

emptystart

If the mailbox is empty S-nail normally prints “No mail for user” and exits immediately. If this option is set S-nail starts even with an empty mailbox.

flipr

This option reverses the meanings of a set of reply commands, turning the lowercase variants, which by default address all recipients included in the header of a message (reply, respond, followup) into the uppercase variants, which by default address the sender only (Reply, Respond, Followup) and vice versa. The commands replysender, respondsender, followupsender as well as replyall, respondall, followupall are not affected by the current setting of flipr.

followup-to

Controls whether a ‘Mail-Followup-To:’ header is generated when sending messages to known mailing lists. Also see followup-to-honour and the commands mlist, mlsubscribe, reply and Lreply.

forward-as-attachment

Original messages are normally sent as inline text with the forward command, and only the first part of a multipart message is included. With this option messages are sent as unmodified MIME ‘message/rfc822’ attachments with all of their parts included.

fullnames

When replying to or forwarding a message S-nail normally removes the comment and name parts of email addresses. If this variable is set such stripping is not performed, and comments, names etc. are retained.

header

Causes the header summary to be written at startup and after commands that affect the number of messages or the order of messages in the current folder; enabled by default. The command line option -N can be used to set noheader.

history-gabby

[Option] Add more entries to the history as is normally done.

history-gabby-persist

[Option] S-nails own NCL will not save the additional (gabby) history entries in persistent storage unless this variable is also set. Also see NAIL_HISTFILE.

hold

This option is used to hold messages in the system mailbox by default.

idna-disable

[Option] Can be used to turn off the automatic conversion of domain names according to the rules of IDNA (internationalized domain names for applications). Since the IDNA code assumes that domain names are specified with the ttycharset character set, an UTF-8 locale charset is required to represent all possible international domain names (before conversion, that is).

ignore

Ignore interrupt signals from the terminal while entering messages; instead echo them as ‘@’ characters and discard the current line.

ignoreeof

Ignore end-of-file conditions (‘control-D’), on message input, which instead can be terminated only by entering a dot ‘.’ on a line by itself or by using the ~. TILDE ESCAPES. This option also applies to S-nail command mode.

imap-use-starttls-USER@HOST, imap-use-starttls-HOST, imap-use-starttls

[Option] Causes S-nail to issue a `STARTTLS' command to make an unencrypted IMAP session SSL/TLS encrypted. This functionality is not supported by all servers, and is not used if the session is already encrypted by the IMAPS method.

keep

If set, an empty mailbox file is not removed. This may improve the interoperability with other mail user agents when using a common folder directory, and prevents malicious users from creating fake mailboxes in a world-writable spool directory. Note this only applies to local regular (MBOX) files, other mailbox types will never be removed.

keepsave

When a message is saved it is usually discarded from the originating folder when S-nail is quit. Setting this option causes all saved message to be retained.

line-editor-disable

Turn off any enhanced command line editing capabilities (see Command line editor for more).

markanswered

When a message is replied to and this variable is set, it is marked as having been answered. This mark has no technical meaning in the mail system; it just causes messages to be marked in the header summary, and makes them specially addressable.

message-id-disable

By setting this option the generation of ‘Message-ID:’ can be completely suppressed, effectively leaving this task up to the mail-transfer-agent (MTA) or the SMTP server. (According to RFC 5321 your SMTP server is not required to add this field by itself, so you should ensure that it accepts messages without a ‘Message-ID’.)

metoo

Usually, when an alias expansion contains the sender, the sender is removed from the expansion. Setting this option suppresses these removals. Note that a set metoo also causes a ‘-m’ option to be passed to mail-transfer-agents (MTAs); though most of the modern MTAs don't (no longer) document this flag, no MTA is known which doesn't support it (for historical compatibility).

mime-allow-text-controls

When sending messages, each part of the message is MIME-inspected in order to classify the ‘Content-Type:’ and ‘Content-Transfer-Encoding:’ (see encoding) that is required to send this part over mail transport, i.e., a computation rather similar to what the file(1) command produces when used with the ‘--mime’ option.

This classification however treats text files which are encoded in UTF-16 (seen for HTML files) and similar character sets as binary octet-streams, forcefully changing any ‘text/plain’ or ‘text/html’ specification to ‘application/octet-stream’: If that actually happens a yet unset charset MIME parameter is set to ‘binary’, effectively making it impossible for the receiving MUA to automatically interpret the contents of the part.

If this option is set, and the data was unambiguously identified as text data at first glance (by a ‘.txt’ or ‘.html’ file extension), then the original ‘Content-Type:’ will not be overwritten.

netrc-lookup-USER@HOST, netrc-lookup-HOST, netrc-lookup

[v15-compat] [Option] Used to control usage of the users .netrc file for lookup of account credentials, as documented in the section On URL syntax and credential lookup and for the command netrc; the section The .netrc file documents the file format.

outfolder

Causes the filename given in the record variable and the sender-based filenames for the Copy and Save commands to be interpreted relative to the directory given in the folder variable rather than to the current directory, unless it is set to an absolute pathname.

page

If set, each message the pipe command prints out is followed by a formfeed character ‘\f’.

piperaw

Send messages to the pipe command without performing MIME and character set conversions.

pop3-bulk-load-USER@HOST, pop3-bulk-load-HOST, pop3-bulk-load

[Option] When accessing a POP3 server S-nail loads the headers of the messages, and only requests the message bodies on user request. For the POP3 protocol this means that the message headers will be downloaded twice. If this option is set then S-nail will download only complete messages from the given POP3 server(s) instead.

pop3-no-apop-USER@HOST, pop3-no-apop-HOST, pop3-no-apop

[Option] Unless this variable is set the ‘APOP’ authentication method will be used when connecting to a POP3 server that advertises support. The advantage of ‘APOP’ is that the password is not sent in clear text over the wire and that only a single packet is sent for the user/password tuple. Note that pop3-no-apop-HOST requires [v15-compat].

pop3-use-starttls-USER@HOST, pop3-use-starttls-HOST, pop3-use-starttls

[Option] Causes S-nail to issue a ‘STLS’ command to make an unencrypted POP3 session SSL/TLS encrypted. This functionality is not supported by all servers, and is not used if the session is already encrypted by the POP3S method. Note that pop3-use-starttls-HOST requires [v15-compat].

print-all-chars

This option causes all characters to be considered printable. It is only effective if given in a startup file. With this option set some character sequences in messages may put the user's terminal in an undefined state when printed; it should only be used as a last resort if no working system locale can be found.

print-alternatives

When a MIME message part of type ‘multipart/alternative’ is displayed and it contains a subpart of type ‘text/plain’, other parts are normally discarded. Setting this variable causes all subparts to be displayed, just as if the surrounding part was of type ‘multipart/mixed’.

quiet

Suppresses the printing of the version when first invoked.

quote-as-attachment

If this is set, then the original message is added in its entirety as a ‘message/rfc822’ MIME attachment when replying to a message. Note this works regardless of the setting of quote.

recipients-in-cc

On group replies, specify only the sender of the original mail in ‘To:’ and mention the other recipients in the secondary ‘Cc:’. By default all recipients of the original mail will be addressed via ‘To:’.

record-resent

If both this variable and the record variable are set, the resend and Resend commands save messages to the record folder as it is normally only done for newly composed messages.

reply-in-same-charset

If this variable is set S-nail first tries to use the same character set of the original message for replies. If this fails, the mechanism described in Character sets is evaluated as usual.

rfc822-body-from_

This variable can be used to force displaying a so-called ‘From_’ line for messages that are embedded into an envelope mail via the ‘message/rfc822’ MIME mechanism, for more visual convenience.

save

Enable saving of (partial) messages in DEAD upon interrupt or delivery error.

searchheaders

Expand message-list specifiers in the form ‘/x:y’ to all messages containing the substring “y” in the header field ‘x’. The string search is case insensitive.

sendcharsets-else-ttycharset

[Option] If this variable is set, but sendcharsets is not, then S-nail acts as if sendcharsets had been set to the value of the variable ttycharset. In effect this combination passes through the message data in the character set of the current locale (given that ttycharset hasn't been set manually), i.e., without converting it to the charset-8bit fallback character set. Thus, mail message text will be in ISO-8859-1 encoding when send from within a ISO-8859-1 locale, and in UTF-8 encoding when send from within an UTF-8 locale. If no character set conversion capabilities are available in S-nail then the only supported character set is ttycharset.

sendmail-no-default-arguments

Unless this option is set S-nail will pass some well known standard command line options to the defined sendmail program, see there for more.

sendwait

When sending a message wait until the MTA (including the builtin SMTP one) exits before accepting further commands. Only with this variable set errors reported by the MTA will be recognizable! If the MTA returns a non-zero exit status, the exit status of s-nail will also be non-zero.

showlast

Setting this option causes S-nail to start at the last message instead of the first one when opening a mail folder.

showname

Causes S-nail to use the sender's real name instead of the plain address in the header field summary and in message specifications.

showto

Causes the recipient of the message to be shown in the header summary if the message was sent by the user.

skipemptybody

If an outgoing message does not contain any text in its first or only message part, do not send it but discard it silently (see also the command line option -E).

smime-force-encryption

[Option] Causes S-nail to refuse sending unencrypted messages.

smime-sign

[Option] S/MIME sign outgoing messages with the user's private key and include the user's certificate as a MIME attachment. Signing a message enables a recipient to verify that the sender used a valid certificate, that the email addresses in the certificate match those in the message header and that the message content has not been altered. It does not change the message text, and people will be able to read the message as usual. Also see smime-sign-cert, smime-sign-include-certs and smime-sign-message-digest.

smime-no-default-ca

[Option] Don't load default CA locations when verifying S/MIME signed messages.

smtp-use-starttls-USER@HOST, smtp-use-starttls-HOST, smtp-use-starttls

[Option] Causes S-nail to issue a ‘STARTTLS’ command to make an SMTP session SSL/TLS encrypted, i.e., to enable transport layer security.

ssl-no-default-ca

[Option] Don't load default CA locations to verify SSL/TLS server certificates.

term-ca-mode

[Option] If terminal capability queries are supported and this option is set then S-nail will try to switch to the “alternate screen” when in interactive mode, so that the terminal will go back to the normal screen, leaving all the text there intact, when S-nail exits. Note: even when supported for this to produce appealing results the used PAGER and possibly configured pipe-TYPE/SUBTYPE applications that take control over the terminal need to have corresponding support too, e.g., the less(1) pager should be driven with the ‘-X’ command line flag.

keep-content-length

When (editing messages and) writing MBOX mailbox files S-nail can be told to keep the ‘Content-Length:’ and ‘Lines:’ header fields that some MUAs generate by setting this variable. Since S-nail does neither use nor update these non-standardized header fields (which in itself shows one of their conceptual problems), stripping them should increase interoperability in between MUAs that work with with same mailbox files. Note that, if this is not set but writebackedited, as below, is, a possibly performed automatic stripping of these header fields already marks the message as being modified.

v15-compat

Setting this option enables upward compatibility with S-nail version 15.0 in respect to which configuration options are available and how they are handled. This manual uses [v15-compat] and [no v15-compat] to refer to the new and the old way of doing things, respectively.

verbose

Setting this option, also controllable via the command line option -v, causes S-nail to be more verbose, so that, e.g., certificate chains will be displayed on the users terminal. Setting this binary option twice increases the level of verbosity, in which case even details of the actual message delivery and protocol conversations are shown. A single noverbose is sufficient to disable verbosity as such.

writebackedited

If this variable is set messages modified using the edit or visual commands are written back to the current folder when it is quit; it is only honoured for writable folders in MBOX format, though. Note that the editor will be pointed to the raw message content in that case, i.e., neither MIME decoding nor decryption will have been performed, and proper RFC 4155 ‘From_’ quoting of newly added or edited content is also left as an excercise to the user.

Value options¶

set 1=val\ one 2="val two" 3='val "three"' 4='val \'four\''
varshow 1 2 3 4
unset 1 2 3 4

Booleans are special string values that must either be set to decimal integers (in which case ‘0’ is false and ‘1’ and any other value is true) or to any of ‘off’, ‘no’ and ‘false’ for a false boolean and ‘on’, ‘yes’ and ‘true’ for a true boolean; matching is performed case-insensitively. And there exists a special kind of boolean, the “quadoption”: this is expected to either name a boolean or one of the strings ‘ask-yes’ and ‘ask-no’ (in fact: ‘ask-’ followed by a valid boolean, case-insensitively); if one of the latter is set then in interactive mode the user will be prompted with the default value (also used for empty user input) set to the given boolean, whereas in non-interactive the given default will be used right away.

agent-shell-lookup-USER@HOST, agent-shell-lookup-HOST, agent-shell-lookup

[v15-compat] [Option] Account passwords can be fetched via an external agent program in order to permit encrypted password storage – see On URL syntax and credential lookup for more on credential lookup. If this is set then the content is interpreted as a shell command the output of which (with newline characters removed) is treated as the account password shall the command succeed (and have produced non-empty non-newline output); e.g., via gpg(1):

$ echo PASSWORD > .pass
$ gpg -e .pass
$ eval `gpg-agent --daemon \
    --pinentry-program=/usr/bin/pinentry-curses \
    --max-cache-ttl 99999 --default-cache-ttl 99999`
$ echo 'set agent-shell-lookup="gpg -d .pass.gpg"' \
    >> ~/.mailrc
    

A couple of environment variables will be set for the agent:

NAIL_TMPDIR

The temporary directory that S-nail uses. Usually identical to TMPDIR, but guaranteed to be set and usable by child processes; to ensure the latter condition for TMPDIR also, it'll be set.

NAIL_USER

The user (‘USER’) for which the password is looked up.

NAIL_USER_ENC

The URL percent-encoded variant of NAIL_USER.

NAIL_HOST

The plain machine hostname of the user account.

NAIL_HOST_PORT

The ‘HOST’ (hostname possibly including port) of the user account.

attrlist

A sequence of characters to print in the ‘attribute’ column of the headline as shown in the header display; each for one type of messages (see Message states), with the default being ‘NUROSPMFAT+-$~’ or ‘NU  *HMFAT+-$~’ if bsdflags or the SYSV3 environment variable are set, in the following order:

‘N’

new.

‘U’

unread but old.

‘R’

new but read.

‘O’

read and old.

‘S’

saved.

‘P’

preserved.

‘M’

mboxed.

‘F’

flagged.

‘A’

answered.

‘T’

draft.

‘+’

start of a collapsed thread.

‘-’

collapsed.

‘$’

classified as spam.

‘~’

classified as possible spam.

autobcc

Specifies a list of recipients to which a blind carbon copy of each outgoing message will be sent automatically.

autocc

Specifies a list of recipients to which a carbon copy of each outgoing message will be sent automatically.

autosort

Causes sorted mode (see the sort command) to be entered automatically with the value of this option as sorting method when a folder is opened.

charset-7bit

The value that should appear in the ‘charset=’ parameter of ‘Content-Type:’ MIME header fields when no character set conversion of the message data was performed. This defaults to US-ASCII, and the chosen character set should be US-ASCII compatible.

charset-8bit

[Option] The default 8-bit character set that is used as an implicit last member of the variable sendcharsets. This defaults to UTF-8. If no character set conversion capabilities are available in S-nail then the only supported character set is ttycharset. Refer to the section Character sets for the complete picture of character set conversion in S-nail.

charset-unknown-8bit

[Option] RFC 1428 specifies conditions when internet mail gateways shall “upgrade” the content of a mail message by using a character set with the name ‘unknown-8bit’. Because of the unclassified nature of this character set S-nail will not be capable to convert this character set to any other character set. If this variable is set any message part which uses the character set ‘unknown-8bit’ is assumed to really be in the character set given in the value, otherwise the (final) value of charset-8bit is used for this purpose.

cmd

The default value for the pipe command.

colour-from_

[Option] The colour specification for so-called ‘From_’ lines. See the section Coloured message display for the format of the value.

colour-header

[Option] The colour specification for header lines.

colour-msginfo

[Option] The colour specification for the introductional message info line.

colour-partinfo

[Option] The colour specification for MIME part info lines.

colour-terms

[Option] A comma-separated list of TERMinals for which coloured message display can be used. Entries only need to be added if the string “color” isn't part of the terminal name itself; the default value is

cons25,linux,rxvt,rxvt-unicode,screen,sun,vt100,vt220,wsvt25,xterm

colour-uheader

[Option] The colour specification for those header lines that have been placed in the colour-user-headers list. See the section Coloured message display.

colour-user-headers

A comma separated list of (case-insensitive) header names which should be colourized with the alternative colour-uheader colours. The default value is ‘from,subject’.

crt

In a(n interactive) terminal session, then if this valued option is set it'll be used as a threshold to determine how many lines the given output has to span before it will be displayed via the configured PAGER; Usage of the PAGER can be forced by setting this to the value ‘0’, setting it without a value will deduce the current height of the terminal screen to compute the treshold (see LINES and stty(1)).

datefield

The date in a header summary is normally the date of the mailbox ‘From_’ line of the message. If this variable is set, then the date as given in the ‘Date:’ field is used, converted to local time. It is possible to control the display of the date by assigning a value, in which case the strftime(3) function will be used to format the date accordingly. Please read your system manual for the available formats. Note that the ‘%n’ format should not be used, because S-nail doesn't take embedded newlines into account when calculating how many lines fit onto the screen.

datefield-markout-older

This option, when set in addition to datefield, is used to display “older” messages (concept is rather comparable to the -l option of the POSIX utility ls(1)). The content interpretation is identical to datefield.

encoding

Suggestion for the MIME encoding to use in outgoing text messages and message parts. Valid values are the default ‘quoted-printable’, ‘8bit’ and ‘base64’. ‘8bit’ may cause problems when transferring mail messages over channels that are not ESMTP (RFC 1869) compliant. If there is no need to encode a message, ‘7bit’ transfer mode is always used regardless of this variable. Binary data is always encoded as ‘base64’.

escape

If defined, the first character of this option gives the character to use in place of ‘~’ to denote TILDE ESCAPES.

expandaddr

If not set then file and command pipeline targets are not allowed, and any such address will be filtered out, giving a warning message. If set without a value then all possible recipient address specifications will be accepted – see the section Sending mail for more on this. To accept them, but only in interactive mode, or when tilde commands were enabled explicitly by using one of the command line options -~ or -#, set this to the (case-insensitive) value ‘restrict’ (note right now this is actually like setting ‘restrict,-all,+name,+addr’).

In fact the value is interpreted as a comma-separated list of values. If it contains ‘fail’ then the existence of disallowed specifications is treated as a hard send error instead of only filtering them out. The remaining values specify whether a specific type of recipient address specification is allowed (optionally indicated by a plus sign ‘+’ prefix) or disallowed (prefixed with a hyphen ‘-’). The value ‘all’ addresses all possible address specifications, ‘file’ file targets, ‘pipe’ command pipeline targets, ‘name’ plain user names and (MTA) aliases ([Obsolete] ‘noalias’ may be used as an alternative syntax to ‘-name’) and ‘addr’ network addresses. These kind of values are interpreted in the given order, so that ‘restrict,fail,+file,-all,+addr’ will cause hard errors for any non-network address recipient address unless S-nail is in interactive mode or has been started with the -~ or -# command line option; in the latter case(s) any address may be used, then.

expandargv

Unless this variable is set additional mail-transfer-agent (MTA) arguments from the command line, as can be given after a ‘--’ separator, are ignored due to safety reasons. However, if set to the special value ‘fail’, then the presence of additional MTA arguments is treated as a hard error that causes S-nail to exit with failure status. A lesser strict variant is the otherwise identical ‘restrict’, which does accept such arguments in interactive mode, or if tilde commands were enabled explicitly by using one of the command line options -~ or -#.

features

(Read-only) Information on the features compiled into S-nail – the content of this variable is identical to the output of the command features.

file-hook-load-EXTENSION, file-hook-save-EXTENSION

It is possible to install file hooks which will be used by the file command in order to be able to transparently handle (through an intermediate temporary file) files with specific ‘EXTENSION’s: the variable values can include shell snippets and are expected to write data to standard output / read data from standard input, respectively. [v15 behaviour may differ] The variables may not be changed while there is a mailbox attendant.

set file-hook-load-xy='echo >&2 XY-LOAD; gzip -cd' \
    file-hook-save-xy='echo >&2 XY-SAVE; gzip -c' \
    record=+null-sent.xy
    

folder

The name of the directory to use for storing folders of messages. All folder names that begin with ‘+’ refer to files below it. The same special conventions as documented for the file command may be used when specifying a new value for folder, but be aware that the expansion is fully performed immediately. E.g., if the expanded name refers to an IMAP account, all names that begin with `+' refer to IMAP mailboxes below the folder target box.

Note: for IMAP it makes a difference whether folder ends with a directory separator solidus or not in respect to the automatic append of `INBOX' strings. Ssome IMAP servers do not accept the creation of mailboxes in the hierarchy base, but require that they are created as subfolders of `INBOX' – with such servers a folder name of the form

imaps://mylogin@imap.myisp.example/INBOX.

should be used (the last character is the server's hierarchy delimiter). Folder names prefixed by `+' will then refer to folders below `INBOX', while folder names prefixed by `@' refer to folders below the hierarchy base. See the imap namespace command for a method to detect the appropriate prefix and delimiter.

folder-hook

When a folder is opened and this variable is set, the macro corresponding to the value of this variable is executed. The macro is also invoked when new mail arrives, but message lists for commands executed from the macro only include newly arrived messages then. If localopts are activated in a folder hook, then the covered settings will be reverted once the folder is left again.

folder-hook-FOLDER

Overrides folder-hook for a folder named ‘FOLDER’. Unlike other folder specifications, the fully expanded name of a folder, without metacharacters, is used to avoid ambiguities. However, if the mailbox resides under folder then the usual ‘+’ specification is tried in addition, e.g., if folder is “mail” (and thus relative to the user's home directory) then /home/usr1/mail/sent will be tried as ‘folder-hook-/home/usr1/mail/sent’ first, but then followed by ‘folder-hook-+sent’.

followup-to-honour

Controls whether a ‘Mail-Followup-To:’ header is honoured when group-replying to a message via reply or Lreply. This is a quadoption; if set without a value it defaults to “yes”. Also see followup-to and the commands mlist and mlsubscribe.

from

The address (or a list of addresses) to put into the ‘From:’ field of the message header, quoting RFC 5322: the author(s) of the message, that is, the mailbox(es) of the person(s) or system(s) responsible for the writing of the message. If replying to messages these addresses are handled as if they were in the alternates list. If the machine's hostname is not valid at the Internet (for example at a dialup machine) then either this variable or hostname ([v15-compat] and with smtp smtp-hostname adds even more fine-tuning capabilities), have to be set. If from contains more than one address, setting the sender variable is required (according to the standard RFC 5322).

fwdheading

The string to print before the text of a message with the forward command (unless the forward-as-attachment variable is set). Defaults to “-------- Original Message --------” if unset; No heading is printed if it is set to the empty string.

headline

A format string to use for the header summary, similar to printf(3) formats. A percent character ‘%’ introduces a format specifier that may be followed by a number indicating the field width; If the (possibly implicitly implied) field width is negative, the field is to be left-aligned. Valid format specifiers are:

‘%%’

A plain percent character.

‘%>’

A space character but for the current message, for which it expands to ‘>’.

‘%<’

A space character but for the current message, for which it expands to ‘<’.

‘%$’

[Option] The spam score of the message, as has been classified via the command spamrate. Prints only a replacement character if there is no spam support.

‘%a’

Message attribute character (status flag); the actual content can be adjusted by setting attrlist.

‘%d’

The date when the message was received.

‘%e’

The indenting level in threaded mode.

‘%f’

The address of the message sender.

‘%i’

The message thread structure. (Note that this format doesn't support a field width.)

‘%l’

The number of lines of the message.

‘%m’

Message number.

‘%o’

The number of octets (bytes) in the message.

‘%s’

Message subject (if any).

‘%S’

Message subject (if any) in double quotes.

‘%T’

Message recipient flags: is the addressee of the message a known or subscribed mailing list – see mlist and mlsubscribe.

‘%t’

The position in threaded/sorted order.

The default is ‘%>%a%m %-18f %16d %4l/%-5o %i%-s’, or ‘%>%a%m %20-f  %16d %3l/%-5o %i%-S’ if bsdcompat is set. Also see attrlist and headline-bidi.

headline-bidi

Bidirectional text requires special treatment when displaying headers, because numbers (in dates or for file sizes etc.) will not affect the current text direction, in effect resulting in ugly line layouts when arabic or other right-to-left text is to be displayed. On the other hand only a minority of terminals is capable to correctly handle direction changes, so that user interaction is necessary for acceptable results. Note that extended host system support is required nonetheless, e.g., detection of the terminal character set is one precondition; and this feature only works in an Unicode (i.e., UTF-8) locale.

In general setting this variable will cause S-nail to encapsulate text fields that may occur when printing headline (and some other fields, like dynamic expansions in prompt) with special Unicode control sequences; it is possible to fine-tune the terminal support level by assigning a value: no value (or any value other than ‘1’, ‘2’ and ‘3’) will make S-nail assume that the terminal is capable to properly deal with Unicode version 6.3, in which case text is embedded in a pair of U+2068 (FIRST STRONG ISOLATE) and U+2069 (POP DIRECTIONAL ISOLATE) characters. In addition no space on the line is reserved for these characters.

Weaker support is chosen by using the value ‘1’ (Unicode 6.3, but reserve the room of two spaces for writing the control sequences onto the line). The values ‘2’ and ‘3’ select Unicode 1.1 support (U+200E, LEFT-TO-RIGHT MARK); the latter again reserves room for two spaces in addition.

hostname

Use this string as hostname when expanding local addresses instead of the value obtained from uname(3) and getaddrinfo(3), i.e., in ‘Message-ID:’ and ‘From:’ fields. Note that when smtp transport is not used then it is normally the responsibility of the MTA to create these fields, [v15-compat] in conjunction with smtp however smtp-hostname also influences the results; you should produce some test messages with the desired combination of hostname, and/or from, sender etc. first.

imap-auth-USER@HOST, imap-auth

[Option] Sets the IMAP authentication method. Valid values are `login' for the usual password-based authentication (the default), `cram-md5', which is a password-based authentication that does not send the password over the network in clear text, and `gssapi' for GSS-API based authentication.

imap-cache

[Option] Enables caching of IMAP mailboxes. The value of this variable must point to a directory that is either existent or can be created by S-nail. All contents of the cache can be deleted by S-nail at any time; it is not safe to make assumptions about them.

imap-delim-USER@HOST, imap-delim-HOST, imap-delim

[Option] The hierarchy separator used by the IMAP server. Whenever an IMAP path is specified it will undergo normalization. One of the normalization steps is the squeeze and adjustment of hierarchy separators. If this variable is set, any occurrence of any character of the given value that exists in the path will be replaced by the first member of the value; an empty value will cause the default to be used, it is ‘/.’. If not set, we will reuse the first hierarchy separator character that is discovered in a user-given mailbox name.

imap-keepalive-USER@HOST, imap-keepalive-HOST, imap-keepalive

[Option] IMAP servers may close the connection after a period of inactivity; the standard requires this to be at least 30 minutes, but practical experience may vary. Setting this variable to a numeric `value' greater than 0 causes a `NOOP' command to be sent each `value' seconds if no other operation is performed.

imap-list-depth

[Option] When retrieving the list of folders on an IMAP server, the folders command stops after it has reached a certain depth to avoid possible infinite loops. The value of this variable sets the maximum depth allowed. The default is 2. If the folder separator on the current IMAP server is a slash `/', this variable has no effect and the folders command does not descend to subfolders.

inbox

If this is set it will be used for expansions of ‘%’, see file for more. [v15 behaviour may differ] IMAP users may set this to the empty string to force bypassing the special handling of folder. The value supports a subset of filename expansions itself.

indentprefix

String used by the ~m, ~M and ~R TILDE ESCAPES and by the quote option for indenting messages, in place of the normal tabulator character ‘^I’, which is the default. Be sure to quote the value if it contains spaces or tabs.

line-editor-cursor-right

[Option] If the builtin command line editor is used, actions which are based on rightwise movement may not work on some terminals. If you encounter such problems, set this variable to the terminal control sequence that is necessary to move the cursor one column to the right. The default is ‘\033[C’, which should work for most terminals. Less often occur ‘\033OC’ and ‘\014’. Note that “Escape” and other control character have to be written as shell-style escape sequences, e.g., ‘\033’ for (US-ASCII) “Escape”.

mime-counter-evidence

Normally the ‘Content-Type:’ field is used to decide how to handle MIME parts. Some MUAs however don't use mime.types(5) or a similar mechanism to correctly classify content, but simply specify ‘application/octet-stream’, even for plain text attachments like ‘text/diff’. If this variable is set then S-nail will try to classify such MIME message parts on its own, if possible, and through their file name. This variable can also be given a non-empty value, in which case the value is expected to be a number, actually a carrier of bits. Creating the bit-carrying number is a simple addition:

? !echo Value should be set to $((2 + 4))
Value should be set to 6
    

• If bit two is set (2) then the detected content-type will be carried along with the message and be used for deciding which pipe-TYPE/SUBTYPE is responsible for the MIME part, shall that question arise; when displaying such a MIME part the part-info will indicate the overridden content-type by showing a plus-sign ‘+’.
• If bit three is set (4) then the counter-evidence is always produced and a positive result will be used as the MIME type, even forcefully overriding the parts given MIME type.

mimetypes-load-control

This option can be used to control which of the mime.types(5) databases are loaded by S-nail, as furtherly described in the section The mime.types files. If the letter ‘u’ is part of the option value, then the user's personal ~/.mime.types file will be loaded (if it exists); likewise the letter ‘s’ controls loading of the system wide /etc/mime.types; the user file is loaded first, letter matching is case-insensitive. If this option is not set S-nail will try to load both files instead. Incorporation of the S-nail-builtin MIME types cannot be suppressed, but they will be matched last.

More sources can be specified by using a different syntax: if the value string contains an equals sign ‘=’ then it is instead parsed as a comma-separated list of the described letters plus ‘f=FILENAME’ pairs; the given filenames will be expanded and loaded, and their content may use the extended syntax that is described in the section The mime.types files.

NAIL_EXTRA_RC

The name of an optional startup file to be read after ~/.mailrc. This variable has an effect only if it is set in s-nail.rc or ~/.mailrc, it is not imported from the environment in order to honour ‘MAILRC=/dev/null/’ -n invocations. Use this file for commands that are not understood by other POSIX mailx(1) implementations.

NAIL_HEAD

A string to put at the beginning of each new message. The escape sequences tabulator ‘\t’ and newline ‘\n’ are understood.

NAIL_HISTFILE

[Option] If a command line editor is available then this can be set to name the (expandable) path of the location of a permanent history file.

NAIL_HISTSIZE

[Option] If a command line editor is available this value restricts the amount of history entries that are saved into a set and valid NAIL_HISTFILE. A value of less than 0 disables this feature; note that loading and incorporation of NAIL_HISTFILE upon program startup can also be suppressed by doing this. An unset or invalid value, or 0, causes a default value to be used. Dependent on the available command line editor this will also define the number of history entries in memory; it is also editor-specific whether runtime updates of this value will be honoured.

NAIL_TAIL

A string to put at the end of each new message. The escape sequences tabulator ‘\t’ and newline ‘\n’ are understood.

newfolders

If this variable has the value ‘maildir’, newly created local folders will be in Maildir format.

newmail

Checks for new mail in the current folder each time the prompt is printed. For IMAP mailboxes the server is then polled for new mail, which may result in delayed operation if the connection to the server is slow. A Maildir folder must be re-scanned to determine if new mail has arrived.

If this variable is set to the special value “nopoll” an IMAP server is not actively asked for new mail, but new mail may still be detected and announced with any other IMAP command that is sent to the server. In either case the IMAP server may send notifications about messages that have been deleted on the server by another process or client. In this case, “Expunged X messages” is printed regardless of this variable, and message numbers may have changed.

If this variable is set to the special value ‘nopoll’ then a Maildir folder will not be rescanned completely, but only timestamp changes are detected.

ORGANIZATION

The value to put into the ‘Organization:’ field of the message header.

password-USER@HOST, password-HOST, password

[v15-compat] Variable chain that sets a password, which is used in case none has been given in the protocol and account-specific URL; as a last resort S-nail will ask for a password on the user's terminal if the authentication method requires a password. Specifying passwords in a startup file is generally a security risk; the file should be readable by the invoking user only.

password-USER@HOST

[no v15-compat] (see the chain above for [v15-compat]) Set the password for ‘USER’ when connecting to ‘HOST’. If no such variable is defined for a host, the user will be asked for a password on standard input. Specifying passwords in a startup file is generally a security risk; the file should be readable by the invoking user only.

pipe-TYPE/SUBTYPE

When a MIME message part of type ‘TYPE/SUBTYPE’ (normalized to lowercase) is displayed or quoted, its text is filtered through the value of this variable interpreted as a shell command. The special value ‘@’ can be used to force interpretation of the message part as plain text, e.g., ‘set pipe-application/pgp-signature=@’ will henceforth treat signatures as plain text and display them "as is". (The same can also be achieved, in a more useful context, by using the mimetype command in conjunction with a type marker.)

Also, if a shell command is prefixed with ‘@’, then the command will only be used to prepare the MIME message part if the message is displayed by itself, but not when multiple messages are displayed at once.

Finally, if a shell command is prefixed with ‘@&’, then, in addition to what has been described for the plain ‘@’ shell command prefix, the command will be run asynchronously, i.e., without blocking S-nail, which may be a handy way to display a, e.g., PDF file while also continuing to read the mail message. Some information about the MIME part to be displayed is embedded into the environment of the shell command:

NAIL_TMPDIR

The temporary directory that S-nail uses. Usually identical to TMPDIR, but guaranteed to be set and usable by child processes; to ensure the latter condition for TMPDIR also, it'll be set.

NAIL_FILENAME

The filename, if any is set, the empty string otherwise.

NAIL_FILENAME_GENERATED

A random string.

NAIL_CONTENT

The MIME content-type of the part, if known, the empty string otherwise.

NAIL_CONTENT_EVIDENCE

If mime-counter-evidence includes the carry-around-bit (2), then this will be set to the detected MIME content-type; not only then identical to NAIL_CONTENT otherwise.

pipe-EXTENSION

This is identical to pipe-TYPE/SUBTYPE except that ‘EXTENSION’ (normalized to lowercase using character mappings of the ASCII charset) names a file extension, e.g., ‘xhtml’. Handlers registered using this method take precedence.

pop3-keepalive-USER@HOST, pop3-keepalive-HOST, pop3-keepalive

[Option] POP3 servers close the connection after a period of inactivity; the standard requires this to be at least 10 minutes, but practical experience may vary. Setting this variable to a numeric value greater than ‘0’ causes a ‘NOOP’ command to be sent each value seconds if no other operation is performed.

prompt

The string printed when a command is accepted. Prompting may be prevented by either setting this to the null string or by setting noprompt. The same XSI escape sequences that are understood by the echo command may be used within prompt.

In addition, the following S-nail specific additional sequences are understood: ‘\&’, which expands to “?” unless bsdcompat is set, in which case it expands to “&”; note that ‘\& ’ is the default value of prompt. ‘\?’, which will expand to “1” if the last command failed and to “0” otherwise, ‘\$’, which will expand to the name of the currently active account, if any, and to the empty string otherwise, and ‘\@’, which will expand to the name of the currently active mailbox. (Note that the prompt buffer is size-limited, excess is cut off.)

Even though prompt checks for headline-bidi to encapsulate the expansions of the ‘\$’ and ‘\@’ escape sequences as necessary to correctly display bidirectional text, this is not true for the final string that makes up prompt as such, i.e., real BIDI handling is not supported.

When a newer version of the editline(3) Command line editor is used, any escape sequence must itself be encapsulated with another escape character for usage with the EL_PROMPT_ESC mechanism: S-nail configures the control character ‘\01’ for this.

quote

If set, S-nail starts a replying message with the original message prefixed by the value of the variable indentprefix. Normally, a heading consisting of “Fromheaderfield wrote:” is printed before the quotation. If the string ‘noheading’ is assigned to the quote variable, this heading is omitted. If the string ‘headers’ is assigned, the headers selected by the ignore/retain commands are printed above the message body, thus quote acts like an automatic `~m' TILDE ESCAPES command, then. If the string ‘allheaders’ is assigned, all headers are printed above the message body and all MIME parts are included, making quote act like an automatic `~M' command; also see quote-as-attachment.

quote-fold

[Option] Can be set in addition to indentprefix. Setting this turns on a more fancy quotation algorithm in that leading quotation characters are compressed and overlong lines are folded. quote-fold can be set to either one or two (space separated) numeric values, which are interpreted as the maximum (goal) and the minimum line length, respectively, in a spirit rather equal to the fmt(1) program, but line-, not paragraph-based. If not set explicitly the minimum will reflect the goal algorithmically. The goal can't be smaller than the length of indentprefix plus some additional pad. Necessary adjustments take place silently.

record

If defined, gives the pathname of the folder used to record all outgoing mail. If not defined, then outgoing mail is not saved. When saving to this folder fails the message is not sent, but instead saved to DEAD.

reply_strings

Can be set to a comma-separated list of (case-insensitive according to ASCII rules) strings which shall be recognized in addition to the builtin strings as ‘Subject:’ reply message indicators – builtin are ‘Re:’, which is mandated by RFC 5322, as well as the german ‘Aw:’.

replyto

A list of addresses to put into the ‘Reply-To:’ field of the message header. Members of this list are handled as if they were in the alternates list.

reply-to-honour

Controls whether a ‘Reply-To:’ header is honoured when replying to a message via reply or Lreply. This is a quadoption; if set without a value it defaults to “yes”.

screen

When S-nail initially prints the message headers it determines the number to print by looking at the speed of the terminal. The faster the terminal, the more it prints. This option overrides this calculation and specifies how many message headers are printed. This number is also used for scrolling with the z command.

sendcharsets

[Option] A comma-separated list of character set names that can be used in outgoing internet mail. The value of the variable charset-8bit is automatically appended to this list of character-sets. If no character set conversion capabilities are compiled into S-nail then the only supported charset is ttycharset. Also see sendcharsets-else-ttycharset and refer to the section Character sets for the complete picture of character set conversion in S-nail.

sender

An address that is put into the ‘Sender:’ field of outgoing messages, quoting RFC 5322: the mailbox of the agent responsible for the actual transmission of the message. This field should normally not be used unless the ‘From:’ field contains more than one address, on which case it is required. The sender address is handled as if it were in the alternates list.

sendmail

To use an alternate mail transport agent (MTA), set this option to the full pathname of the program to use. It may be necessary to set sendmail-progname in addition.

The MTA will be passed command line arguments from several possible sources: from the variable sendmail-arguments if set, from the command line if given and the variable expandargv allows their use. Argument processing of the MTA will be terminated with a ‘--’ separator.

The otherwise occurring implicit usage of the following MTA command line arguments can be disabled by setting the boolean option sendmail-no-default-arguments (which will also disable passing ‘--’ to the MTA): ‘-i’ (for not treating a line with only a dot ‘.’ character as the end of input), ‘-m’ (shall the option metoo be set) and ‘-v’ (if the verbose option is set); in conjunction with the -r command line option S-nail will also pass ‘-f’ as well as ‘-F’.

sendmail-arguments

Arguments to pass through to the Mail-Transfer-Agent can be given via this option. The content of this variable will be split up in a vector of arguments which will be joined onto other possible MTA options:

set sendmail-arguments='-t -X "/tmp/my log"'

sendmail-no-default-arguments

(Binary) Unless this option is set S-nail will pass some well known standard command line options to the defined sendmail program, see there for more.

sendmail-progname

Many systems use a so-called mailwrapper(8) environment to ensure compatibility with sendmail(1). This works by inspecting the name that was used to invoke the mail delivery system. If this variable is set then the mailwrapper (the program that is actually executed when calling “sendmail”) will treat its contents as that name. The default is ‘sendmail’.

Sign

A string for use with the ~A tilde escape.

sign

A string for use with the ~a tilde escape.

signature

Must correspond to the name of a readable file if set. The file's content is then appended to each singlepart message and to the first part of each multipart message. Be warned that there is no possibility to edit the signature for an individual message.

smime-ca-dir

[Option] Specifies a directory with CA certificates in PEM (Privacy Enhanced Mail) format for verification of S/MIME signed messages.

smime-ca-file

[Option] Specifies a file with CA certificates in PEM format for verification of S/MIME signed messages.

smime-cipher-USER@HOST, smime-cipher

[Option] Specifies the cipher to use when generating S/MIME encrypted messages (for the specified account). RFC 5751 mandates a default of ‘aes128’ (AES-128 CBC). Possible values are (case-insensitive and) in decreasing cipher strength: ‘aes256’ (AES-256 CBC), ‘aes192’ (AES-192 CBC), ‘aes128’ (AES-128 CBC), ‘des3’ (DES EDE3 CBC, 168 bits; default if ‘aes128’ isn't available) and ‘des’ (DES CBC, 56 bits).

The actually available cipher algorithms depend on the cryptographic library that S-nail uses. [Option] Support for more cipher algorithms may be available through dynamic loading via, e.g., EVP_get_cipherbyname(3) (OpenSSL) if S-nail has been compiled to support this.

smime-crl-dir

[Option] Specifies a directory that contains files with CRLs in PEM format to use when verifying S/MIME messages.

smime-crl-file

[Option] Specifies a file that contains a CRL in PEM format to use when verifying S/MIME messages.

smime-encrypt-USER@HOST

[Option] If this variable is set, messages send to the given receiver are encrypted before sending. The value of the variable must be set to the name of a file that contains a certificate in PEM format.

If a message is sent to multiple recipients, each of them for whom a corresponding variable is set will receive an individually encrypted message; other recipients will continue to receive the message in plain text unless the smime-force-encryption variable is set. It is recommended to sign encrypted messages, i.e., to also set the smime-sign variable.

smime-sign-cert-USER@HOST, smime-sign-cert

[Option] Points to a file in PEM format. For the purpose of signing and decryption this file needs to contain the user's private key as well as his certificate.

For message signing ‘USER@HOST’ is always derived from the value of from (or, if that contains multiple addresses, sender). For the purpose of encryption the recipient's public encryption key (certificate) is expected; the command certsave can be used to save certificates of signed messages (the section Signed and encrypted messages with S/MIME gives some details). This mode of operation is usually driven by the specialized form.

When decrypting messages the account is derived from the recipient fields (‘To:’ and ‘Cc:’) of the message, which are searched for addresses for which such a variable is set. S-nail always uses the first address that matches, so if the same message is sent to more than one of the user's addresses using different encryption keys, decryption might fail.

smime-sign-include-certs-USER@HOST, smime-sign-include-certs

[Option] If used, this is supposed to a consist of a comma-separated list of files, each of which containing a single certificate in PEM format to be included in the S/MIME message in addition to the smime-sign-cert certificate. This is most useful for long certificate chains if it is desired to aid the receiving party's verification process. Note that top level certificates may also be included in the chain but don't play a role for verification. Also see smime-sign-cert. Remember that for this ‘USER@HOST’ refers to the variable from (or, if that contains multiple addresses, sender).

smime-sign-message-digest-USER@HOST, smime-sign-message-digest

[Option] Specifies the message digest to use when signing S/MIME messages. RFC 5751 mandates a default of ‘sha1’. Possible values are (case-insensitive and) in decreasing cipher strength: ‘sha512’, ‘sha384’, ‘sha256’, ‘sha224’ and ‘md5’.

The actually available message digest algorithms depend on the cryptographic library that S-nail uses. [Option] Support for more message digest algorithms may be available through dynamic loading via, e.g., EVP_get_digestbyname(3) (OpenSSL) if S-nail has been compiled to support this. Remember that for this ‘USER@HOST’ refers to the variable from (or, if that contains multiple addresses, sender).

smtp

[Option] Normally S-nail invokes the program defined via sendmail to transfer messages, as described in Sending mail. Setting the smtp variable will instead cause SMTP network connections be made to the server specified therein in order to directly submit the message. S-nail knows about three different “SMTP protocols”:

• The plain SMTP protocol (RFC 5321) that normally lives on the server port 25 and requires setting the smtp-use-starttls variable to enter a SSL/TLS encrypted session state. Assign a value like [v15-compat] ‘[smtp://][user[:password]@]server[:port]’ ([no v15-compat] ‘[smtp://]server[:port]’) to choose this protocol.
• Then the so-called SMTPS which is supposed to live on server port 465 and is automatically SSL/TLS secured. Unfortunately it never became a standardized protocol and may thus not be supported by your hosts network service database – in fact the port number has already been reassigned to other protocols!

  SMTPS is nonetheless a commonly offered protocol and thus can be chosen by assigning a value like [v15-compat] ‘smtps://[user[:password]@]server[:port]’ ([no v15-compat] ‘smtps://server[:port]’); due to the mentioned problems it is usually necessary to explicitly specify the port as ‘:465’, however.

• Finally there is the SUBMISSION protocol (RFC 6409), which usually lives on server port 587 and is practically identically to the SMTP protocol from S-nails point of view beside that; it requires setting the smtp-use-starttls variable to enter a SSL/TLS secured session state. Assign a value like [v15-compat] ‘submission://[user[:password]@]server[:port]’ ([no v15-compat] ‘submission://server[:port]’).

For more on credentials etc. please see On URL syntax and credential lookup. The SMTP transfer is executed in a child process, which runs asynchronously unless either the sendwait or the verbose variable is set. If it receives a TERM signal, it will abort and save the message to DEAD.

smtp-auth-USER@HOST, smtp-auth-HOST, smtp-auth

[Option] Variable chain that sets the SMTP authentication method. Possible values are ‘none’ ([no v15-compat] default), ‘plain’ ([v15-compat] default), ‘login’ as well as the [Option]al methods ‘cram-md5’ and ‘gssapi’. The ‘none’ method doesn't need any user credentials, ‘gssapi’ requires a user name and all other methods require a user name and a password. See [v15-compat] smtp, user and password ([no v15-compat] smtp-auth-password and smtp-auth-user). Note that smtp-auth-HOST is [v15-compat]. [no v15-compat]: Note for smtp-auth-USER@HOST: may override dependend on sender address in the variable from.

smtp-auth-password

[Option] [no v15-compat] Sets the global fallback password for SMTP authentication. If the authentication method requires a password, but neither smtp-auth-password nor a matching smtp-auth-password-USER@HOST can be found, S-nail will ask for a password on the user's terminal.

smtp-auth-password-USER@HOST

[no v15-compat] Overrides smtp-auth-password for specific values of sender addresses, dependent upon the variable from.

smtp-auth-user

[Option] [no v15-compat] Sets the global fallback user name for SMTP authentication. If the authentication method requires a user name, but neither smtp-auth-user nor a matching smtp-auth-user-USER@HOST can be found, S-nail will ask for a user name on the user's terminal.

smtp-auth-user-USER@HOST

[no v15-compat] Overrides smtp-auth-user for specific values of sender addresses, dependent upon the variable from.

smtp-hostname

[v15-compat] Normally S-nail uses the variable from to derive the necessary ‘USER@HOST’ information to issue a ‘MAIL FROM:<>’ SMTP command. Setting smtp-hostname can be used to use the ‘USER’ from the SMTP account (smtp or the user variable chain) and the ‘HOST’ from the content of this variable (or, if that is the empty string, hostname or the local hostname as a last resort). This often allows using an address that is itself valid but hosted by a provider other than which (in from) is about to send the message. Setting this variable also influences the generated ‘Message-ID:’.

spam-interface

[Option] In order to use any of the spam-related commands (like, e.g., spamrate) the desired spam interface must be defined by setting this variable. Please refer to the manual section Handling spam for the complete picture of spam handling in S-nail. All or none of the following interfaces may be available:

‘spamc’

Interaction with spamc(1) from the spamassassin(1) (SpamAssassin) suite. Different to the generic filter interface S-nail will automatically add the correct arguments for a given command and has the necessary knowledge to parse the program's output. A default value for spamc-command will have been compiled into the S-nail binary if spamc(1) has been found in PATH during compilation. Shall it be necessary to define a specific connection type (rather than using a configuration file for that), the variable spamc-arguments can be used as in, e.g., ‘-d server.example.com -p 783’. It is also possible to specify a per-user configuration via spamc-user. Note that this interface doesn't inspect the ‘is-spam’ flag of a message for the command spamforget.

‘spamd’

S-nail will directly communicate with the spamassassin(1) daemon spamd(1) via a path-based unix(4) stream socket as specified in spamd-socket. It is possible to specify a per-user configuration via spamd-user.

‘filter’

generic spam filter support via freely configurable hooks. This interface is ment for programs like bogofilter(1) and sylfilter(1) and requires according behaviour in respect to the hooks' exit status for at least the command spamrate (‘0’ meaning a message is spam, ‘1’ for non-spam, ‘2’ for unsure and any other return value indicating a hard error); since the hooks can include shell code snippets diverting behaviour can be intercepted as necessary. The hooks are spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate and spamfilter-spam; the manual section Handling spam contains examples for some programs. The process environment of the hooks will have the variables NAIL_TMPDIR, TMPDIR and NAIL_FILENAME_GENERATED set. Note that spam score support for spamrate isn't supported unless the [Option]tional regular expression support is available and the spamfilter-rate-scanscore variable is set.

spam-maxsize

[Option] Messages that exceed this size won't be passed through to the configured spam-interface. The default is 420000 bytes.

spamc-command

[Option] The path to the spamc(1) program for the ‘spamc’ spam-interface. Note that the path is not expanded, but used “as is”. A fallback path will have been compiled into the S-nail binary if the executable had been found during compilation.

spamc-arguments

[Option] Even though S-nail deals with most arguments for the ‘spamc’ spam-interface automatically, it may at least sometimes be desirable to specifiy connection-related ones via this variable, e.g., ‘-d server.example.com -p 783’.

spamc-user

[Option] Specify a username for per-user configuration files for the ‘spamc’ spam-interface. If this is set to the empty string then S-nail will use the name of the current user.

spamd-socket

[Option] Specify the path of the unix(4) domain socket on which spamd(1) listens for connections for the ‘spamd’ spam-interface. Note that the path is not expanded, but used “as is”.

spamd-user

[Option] Specify a username for per-user configuration files for the ‘spamd’ spam-interface. If this is set to the empty string then S-nail will use the name of the current user.

spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate, spamfilter-spam

[Option] Command and argument hooks for the ‘filter’ spam-interface. The manual section Handling spam contains examples for some programs.

spamfilter-rate-scanscore

[Option] Because of the generic nature of the ‘filter’ spam-interface spam scores are not supported for it by default, but if the [Option]tional regular expression support is available then setting this variable can be used to overcome this restriction. It is interpreted as follows: first a number (digits) is parsed that must be followed by a semicolon ‘;’ and a regular expression. Then the latter is used to parse the first output line of the spamfilter-rate hook, and, in case the evaluation is successful, the group that has been specified via the number is interpreted as a floating point scan score.

ssl-ca-dir

[Option] Specifies a directory with CA certificates in PEM (Pricacy Enhanced Mail) for verification of of SSL/TLS server certificates. See SSL_CTX_load_verify_locations(3) for more information.

ssl-ca-file

[Option] Specifies a file with CA certificates in PEM format for verification of SSL/TLS server certificates. See SSL_CTX_load_verify_locations(3) for more information.

ssl-cert-USER@HOST, ssl-cert-HOST, ssl-cert

[Option] Variable chain that sets the file name for a SSL/TLS client certificate required by some servers. This is a direct interface to the ‘Certificate’ slot of the SSL_CONF_cmd(3) function of the OpenSSL library, if available.

ssl-cipher-list-USER@HOST, ssl-cipher-list-HOST, ssl-cipher-list

[Option] Specifies a list of ciphers for SSL/TLS connections. This is a direct interface to the ‘CipherString’ slot of the SSL_CONF_cmd(3) function of the OpenSSL library, if available; see ciphers(1) for more information. By default S-nail doesn't set a list of ciphers, which in effect will use a ssl-protocol specific cipher (protocol standards ship with a list of acceptable ciphers), possibly cramped to what the actually used SSL/TLS library supports – the manual section An example configuration also contains a SSL/TLS use case.

ssl-config-file

[Option] If this variable is set S-nail will call CONF_modules_load_file(3) to allow OpenSSL to be configured according to the host system wide security settings. If a non-empty value is given then this will be used to specify the configuration file to be used instead of the global OpenSSL default; note that in this case it is an error if the file cannot be loaded. The application name will always be passed as “s-nail”.

ssl-crl-file

[Option] Specifies a file that contains a CRL in PEM format to use when verifying SSL/TLS server certificates.

ssl-crl-dir

[Option] Specifies a directory that contains files with CRLs in PEM format to use when verifying SSL/TLS server certificates.

ssl-key-USER@HOST, ssl-key-HOST, ssl-key

[Option] Variable chain that sets the file name for the private key of a SSL/TLS client certificate. If unset, the name of the certificate file is used. The file is expected to be in PEM format. This is a direct interface to the ‘PrivateKey’ slot of the SSL_CONF_cmd(3) function of the OpenSSL library, if available.

ssl-method-USER@HOST, ssl-method-HOST, ssl-method

[Option] [Obsolete] Please use the newer and more flexible ssl-protocol instead: if both values are set, ssl-protocol will take precedence! Can be set to the following values, the actually used ssl-protocol specification to which it is mapped is shown in parenthesis: ‘tls1.2’ (‘-ALL, TLSv1.2’), ‘tls1.1’ (‘-ALL, TLSv1.1’), ‘tls1’ (‘-ALL, TLSv1’) and ‘ssl3’ (‘-ALL, SSLv3’); the special value ‘auto’ is mapped to ‘ALL, -SSLv2’ and thus includes the SSLv3 protocol. Note that SSLv2 is no longer supported at all.

ssl-protocol-USER@HOST, ssl-protocol-HOST, ssl-protocol

[Option] Specify the used SSL/TLS protocol. This is a direct interface to the ‘Protocol’ slot of the SSL_CONF_cmd(3) function of the OpenSSL library, if available; otherwise an S-nail internal parser is used which understands the following subset of (case-insensitive) command strings: ‘SSLv3’, ‘TLSv1’, ‘TLSv1.1’ and ‘TLSv1.2’, as well as the special value ‘ALL’. Multiple specifications may be given via a comma-separated list which ignores any whitespace. An optional ‘+’ plus prefix will enable a protocol, a ‘-’ minus prefix will disable it, so that ‘-ALL, TLSv1.2’ will enable only the TLSv1.2 protocol.

It depends upon the used TLS/SSL library which protocols are actually supported and which protocols are used if ssl-protocol is not set, but note that SSLv2 is no longer supported at all and actively disabled. Especially for older protocols explicitly securing ssl-cipher-list may be worthwile, see An example configuration.

ssl-rand-egd

[Option] Gives the pathname to an entropy daemon socket, see RAND_egd(3). Not all SSL/TLS libraries support this.

ssl-rand-file

[Option] Gives the pathname to a file with entropy data, see RAND_load_file(3). If the file is a regular file writable by the invoking user, new data is written to it after it has been loaded.

ssl-verify-USER@HOST, ssl-verify-HOST, ssl-verify

[Option] Variable chain that sets the action to be performed if an error occurs during SSL/TLS server certificate validation. Valid (case-insensitive) values are ‘strict’ (fail and close connection immediately), ‘ask’ (ask whether to continue on standard input), ‘warn’ (print a warning and continue), ‘ignore’ (do not perform validation). The default is ‘ask’.

stealthmua

If only set without an assigned value, then this option inhibits the generation of the ‘Message-ID:’ and ‘User-Agent:’ header fields that include obvious references to S-nail. There are two pitfalls associated with this: First, the message id of outgoing messages is not known anymore. Second, an expert may still use the remaining information in the header to track down the originating mail user agent. If set to the value ‘noagent’, then the mentioned ‘Message-ID:’ suppression doesn't occur.

toplines

If defined, gives the number of lines of a message to be printed out with the top command; normally, the first five lines are printed.

ttycharset

The character set of the terminal S-nail operates on, and the one and only supported character set that S-nail can use if no character set conversion capabilities have been compiled into it, in which case it defaults to ISO-8859-1 unless it can deduce a value from the LC_CTYPE locale environment. Refer to the section Character sets for the complete picture about character sets.

user-HOST, user

[v15-compat] Variable chain that sets a global fallback user name, which is used in case none has been given in the protocol and account-specific URL. This variable defaults to the value of USER.

version, version-major, version-minor, version-update

(Read-only) S-nail version information: the first variable contains a string containing the complete version identification – this is identical to the output of the command version. The latter three contain only digits: the major, minor and update version numbers.

The mime.types files¶

It learns about MIME types and how to treat them by reading mime.types files, the loading of which can be controlled by setting the variable mimetypes-load-control. (The command mimetype can also be used to deal with MIME types.) mime.types files have the following syntax:

where ‘type/subtype’ are strings describing the file contents, and one or multiple ‘extension’s, separated by whitespace, name the part of a filename starting after the last dot (of interest). Comments may be introduced anywhere on a line with a number sign ‘#’, causing the remaining line to be discarded. S-nail also supports an extended, non-portable syntax in specially crafted files, which can be loaded via the alternative value syntax of mimetypes-load-control and prepends an optional ‘type-marker’:

The following type markers are supported:

Further reading: for sending messages: mime-allow-text-controls. For reading etc. messages: Viewing HTML mail and MIME attachments, mime-counter-evidence, pipe-TYPE/SUBTYPE, pipe-EXTENSION.

The .netrc file¶

• BSD doesn't support single, but only double quotation marks, e.g., ‘password="pass with spaces"’.
• BSD (only?) supports escaping of single characters via a backslash (e.g., a space can be escaped via ‘\ ’), in- as well as outside of a quoted string.
• BSD doesn't require the final quotation mark of the final user input token.
• At least Hewlett-Packard seems to support a format which also allows tokens to be separated with commas – this format is not supported!
• Whereas other programs may require that the .netrc file is accessible by only the user if it contains a password token for any other login than “anonymous”, S-nail will always require these strict permissions.

Of the following list of supported tokens S-nail only uses (and caches) machine, login and password:

machine name

The hostname of the entries' machine, lowercase-normalized by S-nail before use. Any further file content, until either end-of-file or the occurrence of another machine or a default first-class token is bound (only related) to the machine name.

As an extension that shouldn't be the cause of any worries S-nail supports a single wildcard prefix for name:

machine *.example.com login USER password PASS
machine pop3.example.com login USER password PASS
machine smtp.example.com login USER password PASS
    

which would match ‘xy.example.com’ as well as ‘pop3.example.com’, but neither ‘example.com’ nor ‘local.smtp.example.com’. Note that in the example neither ‘pop3.example.com’ nor ‘smtp.example.com’ will be matched by the wildcard, since the exact matches take precedence (it is however faster to specify it the other way around).

default

This is the same as machine except that it is a fallback entry that is used shall none of the specified machines match; only one default token may be specified, and it must be the last first-class token.

login name

The user name on the remote machine.

password string

The user's password on the remote machine.

account string

Supply an additional account password. This is merely for FTP purposes.

macdef name

Define a macro. A macro is defined with the specified name; it is formed from all lines beginning with the next line and continuing until a blank line is (consecutive newline characters are) encountered. (Note that macdef entries cannot be utilized by multiple machines, too, but must be defined following the machine they are intended to be used with.) If a macro named init exists, it is automatically run as the last step of the login process. This is merely for FTP purposes.

An example configuration¶

# This example assumes v15.0 compatibility mode
set v15-compat

# Where are the up-to-date SSL certificates?
#set ssl-ca-dir=/etc/ssl/certs
set ssl-ca-file=/etc/ssl/certs/ca-certificates.crt

# (Since we manage up-to-date ones explicitly, don't use any,
# possibly outdated, default certificates shipped with OpenSSL
set ssl-no-default-ca

# Don't use protocols olders than TLS v1.2.
# Change this only when the remote server doesn't support it:
# maybe use ssl-protocol-HOST (or -USER@HOST) syntax to define
# such explicit exceptions, then
set ssl-protocol="-ALL,+TLSv1.2"

# Explicitly define the list of ciphers, which may improve security,
# especially with protocols older than TLS v1.2.  See ciphers(1).
# Hint: it is important to include "@STRENGTH": only with it the
# final list will be sorted by algorithm strength.
# This is an example: in reality it is possibly best to only use
# ssl-cipher-list-HOST (or -USER@HOST), as necessary, again..
set ssl-cipher-list="ALL:!aNULL:!MEDIUM:!LOW:\
    !MD5:!RC4:!EXPORT:@STRENGTH"

# Request strict transport security checks!
set ssl-verify=strict

# Essential setting: select allowed character sets
set sendcharsets=utf-8,iso-8859-1

# A very kind option: when replying to a message, first try to
# use the same encoding that the original poster used herself!
set reply-in-same-charset

# When replying to or forwarding a message the comment and name
# parts of email addresses are removed unless this variable is set
set fullnames

# When sending messages, wait until the Mail-Transfer-Agent finishs.
# Only like this you'll be able to see errors reported through the
# exit status of the MTA (including the builtin SMTP one)!
set sendwait

# Only use builtin MIME types, no mime.types(5) files
set mimetypes-load-control

# Default directory where we act in (relative to $HOME)
set folder=mail MBOX=+mbox.mbox record=+sent.mbox \
    DEAD=+dead.mbox

# Make "file mymbox" and "file myrec" go to..
shortcut mymbox %:+mbox.mbox myrec +sent.mbox

# Not really optional, e.g., for S/MIME
set from="Your Name <youremail@domain>"

# It may be necessary to set hostname and/or smtp-hostname
# if the "SERVER" of smtp and "domain" of from don't match.
# The `urlcodec' command can be used to encode USER and PASS
set smtp=(smtp[s]/submission)://[USER[:PASS]@]SERVER[:PORT] \
    smtp-auth=login/plain... \
    smtp-use-starttls

# Never refuse to start into interactive mode, and more
set emptystart \
    colour-pager crt= followup-to followup-to-honour=ask-yes \
    history-gabby mime-counter-evidence=6 \
    prompt="\033[31m?\?[\$ \@]\& \033[0m" \
    NAIL_HISTFILE=+.s-nailhist NAIL_HISTSIZE=-1 \
    reply-to-honour=ask-yes

# When `p'rinting messages, show only these headers
# (use `P'rint for all headers and `S'how for raw message)
retain date from to cc subject

# Some mailing lists
mlist @xyz-editor.xyz$ @xyzf.xyz$
mlsubscribe ^xfans@xfans.xyz$

# A real life example of a very huge free mail provider
account XooglX {
  localopts yes
  set from="Your Name <youremail@domain>"
  # (The plain smtp:// proto is optional)
  set smtp=USER:PASS@smtp.gmXil.com smtp-use-starttls
}

# Here is a pretty large one which does not allow sending mails
# if there is a domain name mismatch on the SMTP protocol level,
# which would bite us if the value of from does not match, e.g.,
# for people who have a sXXXXeforge project and want to speak
# with the mailing list under their project account (in from),
# still sending the message through their normal mail provider
account XandeX {
  localopts true
  set from="Your Name <youremail@domain>"
  set smtp=smtps://USER:PASS@smtp.yaXXex.ru:465 \
      hostname=yaXXex.com smtp-hostname=
}

# Create some new commands so that, e.g., `ls /tmp' will..
ghost l   !ls -aFtr
ghost L   !ls -aFt
ghost ll  !ls -aFltr
ghost Ll  !ls -aFlt
ghost la  !ls -aFr
ghost La  !ls -aF
ghost lla !ls -aFlr
ghost Lla !ls -aFl
ghost lS  !ls -aFrS
ghost LS  !ls -aFS
ghost llS !ls -aFlrS
ghost LlS !ls -aFlS

# We don't support gpg(1) directly yet.  But simple --clearsign'd
# message parts can be dealt with as follows:
define V {
  localopts yes
  set pipe-text/plain="set -C;\
    : > \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\" \
    trap \"rm -f \\\"${TMPDIR}/${NAIL_FILENAME_GENERATED}\\\"\" \
      EXIT INT QUIT PIPE TERM;\
    set +C;\
    cat > \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\";\
    < \"${TMPDIR}/${NAIL_FILENAME_GENERATED}\" awk \
        -v TMPFILE=\"${TMPDIR}/${NAIL_FILENAME_GENERATED}\" '\
      BEGIN {done=0}\
      /^-----BEGIN PGP SIGNED MESSAGE-----/,/^$/ {\
        if (done++ != 0)\
          next;\
        print \"--- GPG --verify ---\";\
        system(\"gpg --verify \" TMPFILE \" 2>&1\");\
        print \"--- GPG --verify ---\";\
        print \"\";\
        next;\
      }\
      /^-----BEGIN PGP SIGNATURE-----/,\
          /^-----END PGP SIGNATURE-----/ {\
        next;\
      }\
      {print}\
      '"
  print
}
ghost V call V

define RK {
  !printf 'Key IDs to gpg --recv-keys: ';\
    read keyids;\
    gpg --recv-keys ${keyids};
}
ghost RK call RK

When storing passwords in ~/.mailrc appropriate permissions should be set on this file with ‘$ chmod 0600 ~/.mailrc’. If the [Option]al netrc-lookup is available user credentials can be stored in the central .netrc file instead; e.g., here is a different version of the example account that sets up SMTP and POP3:

account XandeX {
  localopts true
  set from="Your Name <youremail@domain>"
  set netrc-lookup
  #set agent-shell-lookup="gpg -d .pass.gpg"

  set smtp=smtps://smtp.yXXXXx.ru:465 \
      smtp-hostname= hostname=yXXXXx.com
  set pop3-keepalive=240 pop3-no-apop-pop.yXXXXx.ru
  ghost xp fi pop3s://pop.yXXXXx.ru
}

and, in the .netrc file:

machine *.yXXXXx.ru login USER password PASS

If the also [Option]al agent-shell-lookup is available things could be diversified further by using encrypted password storage: for this, don't specify ‘password PASS’ in the .netrc file and instead uncomment the line that defines agent lookup in the example account above, then create the encrypted password storage file .pass.gpg:

$ echo PASS > .pass
$ gpg -e .pass
$ eval `gpg-agent --daemon \
        --pinentry-program=/usr/bin/pinentry-curses \
        --max-cache-ttl 99999 --default-cache-ttl 99999`

This configuration should now work just fine (use the -d command line option for a(n almost) dry-run):

Signed and encrypted messages with S/MIME¶

It is thus usually possible to sign all outgoing messages if so desired. Encryption, in contrast, makes the message text invisible for all people except those who have access to the secret decryption key. To encrypt a message, the specific recipient's public encryption key must be known. It is therefore not possible to send encrypted mail to people unless their key has been retrieved from either previous communication or public key directories. A message should always be signed before it is encrypted. Otherwise, it is still possible that the encrypted message text is altered.

A central concept to S/MIME is that of the certification authority (CA). A CA is a trusted institution that issues certificates. For each of these certificates it can be verified that it really originates from the CA, provided that the CA's own certificate is previously known. A set of CA certificates is usually delivered with OpenSSL and installed on your system. If you trust the source of your OpenSSL software installation, this offers reasonable security for S/MIME on the Internet. (Otherwise set ssl-no-default-ca and use smime-ca-file and/or smime-ca-dir.) In general, a certificate cannot be more secure than the method its CA certificate has been retrieved with, though. Thus if you download a CA certificate from the Internet, you can only trust the messages you verify using that certificate as much as you trust the download process.

The first thing you need for participating in S/MIME message exchange is your personal certificate, including a private key. The certificate contains public information, in particular your name and your email address(es), and the public key that is used by others to encrypt messages for you, and to verify signed messages they supposedly received from you. The certificate is included in each signed message you send. The private key must be kept secret. It is used to decrypt messages that were previously encrypted with your public key, and to sign messages.

For personal use it is recommended that you get a S/MIME certificate from one of the major CAs on the Internet using your WWW browser. Many CAs offer such certificates for free. There is also https://www.CAcert.org which issues client and server certificates to members of their community for free; their root certificate (https://www.cacert.org/certs/root.crt) is often not in the default set of trusted CA root certificates, though, which means you will have to download their root certificate separately and ensure it is part of our S/MIME certificate validation chain by including it in smime-ca-dir or as a vivid member of the smime-ca-file. But let's take a step-by-step tour on how to setup S/MIME with a certificate from CAcert.org despite this situation!

First of all you will have to become a member of the CAcert.org community, simply by registrating yourself via the web interface. Once you are, create and verify all email addresses you want to be able to create signed and encrypted messages for/with using the corresponding entries of the web interface. Now ready to create S/MIME certificates, so let's create a new “client certificate”, ensure to include all email addresses that should be covered by the certificate in the following web form, and also to use your name as the “common name”.

Create a private key and a certificate request on your local computer (please see the manual pages of the used commands for more in-depth knowledge on what the used arguments etc. do):

Afterwards copy-and-paste the content of “creq.pem” into the certificate-request (CSR) field of the web form on the CAcert.org website (you may need to unfold some “advanced options” to see the corresponding text field). This last step will ensure that your private key (which never left your box) and the certificate belong together (through the public key that will find its way into the certificate via the certificate-request). You are now ready and can create your CAcert certified certificate. Download and store or copy-and-paste it as “pub.crt”.

Yay. In order to use your new S/MIME setup you will have to create a combined private key/public key (certificate) file:

This is the file S-nail will work with. If you have created your private key with a passphrase then S-nail will ask you for it whenever a message is signed or decrypted. Set the following variables to henceforth use S/MIME (setting smime-ca-file is of interest for verification only):

set smime-ca-file=ALL-TRUSTED-ROOT-CERTS-HERE \
  smime-sign-cert=ME@HERE.com.paired \
  smime-sign-message-digest=SHA256 \
  smime-sign

From each signed message you send, the recipient can fetch your certificate and use it to send encrypted mail back to you. Accordingly if somebody sends you a signed message, you can do the same, and use the verify command to check the validity of the certificate.

Options of interest for S/MIME signing: smime-ca-dir, smime-ca-file, smime-crl-dir, smime-crl-file, smime-no-default-ca, smime-sign, smime-sign-cert, smime-sign-include-certs and smime-sign-message-digest.

After it has been verified save the certificate via certsave and tell S-nail that it should use it for encryption for further communication with that somebody:

certsave FILENAME
set smime-encrypt-USER@HOST=FILENAME \
    smime-cipher-USER@HOST=AES256

Additional options of interest for S/MIME en- and decryption: smime-cipher and smime-encrypt-USER@HOST.

You should carefully consider if you prefer to store encrypted messages in decrypted form. If you do, anybody who has access to your mail folders can read them, but if you do not, you might be unable to read them yourself later if you happen to lose your private key. The decrypt command saves messages in decrypted form, while the save, copy, and move commands leave them encrypted.

Note that neither S/MIME signing nor encryption applies to message subjects or other header fields yet. Thus they may not contain sensitive information for encrypted messages, and cannot be trusted even if the message content has been verified. When sending signed messages, it is recommended to repeat any important header information in the message text.

Using CRLs with S/MIME or SSL/TLS¶

S-nail accepts CRLs in PEM format only; CRLs in DER format must be converted, like, e.g.:

To tell S-nail about the CRLs, a directory that contains all CRL files (and no other files) must be created. The smime-crl-dir or ssl-crl-dir variables, respectively, must then be set to point to that directory. After that, S-nail requires a CRL to be present for each CA that is used to verify a certificate.

Handling spam¶

• spamrate rates the given messages and sets their ‘is-spam’ flag accordingly. If the spam interface offers spam scores those can also be displayed in the header display by including the ‘%$’ format in the headline variable.
• spamham, spamspam and spamforget will interact with the Bayesian filter of the chosen interface and learn the given messages as “ham” or “spam”, respectively; the last command can be used to cause “unlearning” of messages; it adheres to their current ‘is-spam’ state and thus reverts previous teachings.
• spamclear and spamset will simply set and clear, respectively, the mentioned volatile ‘is-spam’ message flag, without any interface interaction.

The spamassassin(1) based spam-interfaces ‘spamc’ and ‘spamd’ require a running instance of the spamd(1) server in order to function, started with the option --allow-tell shall Bayesian filter learning be possible. ‘spamd’ only works via a local path-based unix(4) socket, but otherwise the following will be equivalently fine:

$ spamd -i localhost:2142 -i /tmp/.spamsock -d [-L] [-l]
$ spamd --listen=localhost:2142 --listen=/tmp/.spamsock \
    --daemonize [--local] [--allow-tell]

Thereafter S-nail can make use of these interfaces:

$ s-nail -Sspam-interface=spamd -Sspam-maxsize=500000 \
    -Sspamd-socket=/tmp/.spamsock -Sspamd-user=

$ s-nail -Sspam-interface=spamc -Sspam-maxsize=500000 \
    -Sspamc-command=/usr/local/bin/spamc \
    -Sspamc-arguments="-U /tmp/.spamsock" -Sspamc-user=
or
$ s-nail -Sspam-interface=spamc -Sspam-maxsize=500000 \
    -Sspamc-command=/usr/local/bin/spamc \
    -Sspamc-arguments="-d localhost -p 2142" -Sspamc-user=

Using the generic filter approach allows usage of programs like bogofilter(1) and sylfilter(1). Here is an example for the former, requiring it to be accessible via PATH:

$ s-nail -Sspam-interface=filter -Sspam-maxsize=500000 \
    -Sspamfilter-ham="bogofilter -n" \
    -Sspamfilter-noham="bogofilter -N" \
    -Sspamfilter-nospam="bogofilter -S" \
    -Sspamfilter-rate="bogofilter -TTu 2>/dev/null" \
    -Sspamfilter-spam="bogofilter -s" \
    -Sspamfilter-rate-scanscore="1;^(.+)$"

Because messages must exist on local storage in order to be scored (or used for Bayesian filter training), it is possibly a good idea to perform the local spam check last:

define spamdelhook {
  # Server side DCC
  spamset (header x-dcc-brand-metrics "bulk")
  # Server-side spamassassin(1)
  spamset (header x-spam-flag "YES")
  del :s # TODO we HAVE to be able to do `spamrate :u ! :sS'
  move :S +maybe-spam
  spamrate :u
  del :s
  move :S +maybe-spam
}
set folder-hook-FOLDER=spamdelhook

See also the documentation for the variables spam-interface, spam-maxsize, spamc-command, spamc-arguments, spamc-user, spamd-socket, spamd-user, spamfilter-ham, spamfilter-noham, spamfilter-nospam, spamfilter-rate and spamfilter-rate-scanscore.

S-nail shortly hangs on startup¶

I can't login to Google mail a.k.a. GMail¶

Different to Kerberos / GSSAPI, which is developed since the mid of the 1980s, where a user can easily create a local authentication ticket for her- and himself with the locally installed kinit(1) program, that protocol has no such local part but instead requires a world-wide-web query to create or fetch a token; since there is no local cache this query has to be performed whenever S-nail is invoked from the command line (in interactive sessions situation may differ).

S-nail doesn't support OAuth. Because of this it is necessary to declare S-nail a “less secure app” (on the providers account web page) in order to read and send mail. However, it also seems possible to take the following steps instead:

1. give the provider the number of a mobile phone,
2. enable “2-Step Verification”,
3. create an application specific password (16 characters), and
4. use that special password instead of your real Google account password in S-nail (for more on that see the section On URL syntax and credential lookup).