slocal - asynchronously filter and deliver new mail to nmh
/usr/lib/mh/slocal [-help] [-version] [-addr address] [-info data] [-sender sender] [-user username] [-mailbox mbox] [-file file] [-maildelivery deliveryfile] [-verbose | -noverbose] [-suppressdup | -nosuppressdup] [-debug]
slocal is a program designed to allow you to have your inbound mail processed according to a complex set of selection criteria. You do not normally invoke slocal yourself, rather slocal is invoked on your behalf by your system's Message Transfer Agent (such as sendmail) when the message arrives.
The message selection criteria used by slocal is specified in the file “.maildelivery” in the user's home directory. You can specify an alternate file with the -maildelivery file option. The syntax of this file is specified below.
The message delivery address and message sender are determined from the Message Transfer Agent envelope information, if possible. Under sendmail, the sender will obtained from the UUCP “From:” line, if present. The user may override these values with the -addr and -sender switches.
The message is normally read from the standard input. The -file switch sets the name of the file from which the message should be read, instead of reading stdin. This is useful when debugging a “.maildelivery” file.
The -user switch tells slocal the name of the user for whom it is delivering mail. It must exist on the local system. The -mailbox switch tells slocal the name of the user's mail drop file.
slocal is able to detect and suppress duplicate messages. To enable this, use the option -suppressdup. slocal will keep a database containing the Message-ID's of incoming messages, in order to detect duplicates. Depending on your configuration, this database will be in either ndbm or Berkeley db format.
The -info switch may be used to pass an arbitrary argument to sub-processes which slocal may invoke on your behalf.
The -verbose switch causes slocal to give information on stdout about its progress. The -debug switch produces more verbose debugging output on stderr. These flags are useful when creating and debugging your “.maildelivery” file, as they allow you to see the decisions and actions that slocal is taking, as well as check for syntax errors in your “.maildelivery” file.
Message Transfer Agents¶
Most modern MTAs including sendmail, postfix and exim support a .forward file for directing incoming mail. You should include the line
“| /usr/lib/mh/slocal -user username”
in your .forward file in your home directory. This will cause your MTA to invoke slocal on your behalf when a message arrives.
The Maildelivery File¶
The “.maildelivery” file controls how slocal filters and delivers incoming mail. Each line of this file consists of five fields, separated by whitespace or comma. Since double-quotes are honored, these characters may be included in a single argument by enclosing the entire argument in double-quotes. A double-quote can be included by preceding it with a backslash. Lines beginning with `#' and blank lines are ignored.
The format of each line in the “.maildelivery” file is:
The following special fields are also defined:
- This action always succeeds.
- file, mbox, or >
- Append the message to the file named by string. The message is appended to the file in mbox (uucp) format. This is the format used by most other mail clients (such as mailx, elm). If the message can be appended to the file, then this action succeeds.
- Identical to file, but always appends the message using the MMDF mailbox format.
- pipe or |
- Pipe the message as the standard input to the command named by string, using the Bourne shell sh to interpret the string. Prior to giving the string to the shell, it is expanded with the following built-in variables:
- the out-of-band sender information
- the address that was used to cause delivery to the recipient
- the size of the message in bytes
- either the “Reply-To:” or “From:” field of the message
- the out-of-band information specified
- qpipe or ^
- Similar to pipe, but executes the command directly, after built-in variable expansion, without assistance from the shell. This action can be used to avoid quoting special characters which your shell might interpret.
- folder or +
- Store the message in the nmh folder named by string. Currently this is handled by piping the message to the nmh program rcvstore, although this may change in the future.
- Perform the action. If the action succeeds, then the message is considered delivered.
- Perform the action. Regardless of the outcome of the action, the message is not considered delivered.
- Perform the action only if the message has not been delivered. If the action succeeds, then the message is considered delivered.
- Perform the action only if the message has not been delivered and the previous action succeeded. If this action succeeds, then the message is considered delivered.
The delivery file is always read completely, so that several matches can be made and several actions can be taken.
Security of Delivery Files¶
In order to prevent security problems, the “.maildelivery” file must be owned either by the user or by root, and must be writable only by the owner. If this is not the case, the file is not read.
If the “.maildelivery” file cannot be found, or does not perform an action which delivers the message, then slocal will check for a global delivery file at /etc/nmh/maildelivery. This file is read according to the same rules. This file must be owned by root and must be writable only by root.
If a global delivery file cannot be found or does not perform an action which delivers the message, then standard delivery to the user's mail drop is performed.
Example Delivery File¶
To summarize, here's an example delivery file:
# # .maildelivery file for nmh's slocal # # Blank lines and lines beginning with a '#' are ignored # # FIELD PATTERN ACTION RESULT STRING # # File mail with foobar in the “To:” line into file foobar.log To foobar file A foobar.log # Pipe messages from coleman to the program message-archive From coleman pipe A /bin/message-archive # Anything to the “nmh-workers” mailing list is put in # its own folder, if not filed already To nmh-workers folder ? nmh-workers # Anything with Unix in the subject is put into # the file unix-mail Subject unix file A unix-mail # I don't want to read mail from Steve, so destroy it From steve destroy A - # Put anything not matched yet into mailbox default - file ? mailbox # always run rcvtty * - pipe R /usr/lib/mh/rcvtty
When a process is invoked, its environment is: the user/group-ids are set to recipient's ids; the working directory is the recipient's home directory; the umask is 0077; the process has no /dev/tty; the standard input is set to the message; the standard output and diagnostic output are set to /dev/null; all other file-descriptors are closed; the environment variables $USER, $HOME, $SHELL are set appropriately, and no other environment variables exist.
The process is given a certain amount of time to execute. If the process does not exit within this limit, the process will be terminated with extreme prejudice. The amount of time is calculated as ((size / 60) + 300) seconds, where size is the number of bytes in the message (with 30 minutes the maximum time allowed).
The exit status of the process is consulted in determining the success of the action. An exit status of zero means that the action succeeded. Any other exit status (or abnormal termination) means that the action failed.
In order to avoid any time limitations, you might implement a process that began by fork()-ing. The parent would return the appropriate value immediately, and the child could continue on, doing whatever it wanted for as long as it wanted. This approach is somewhat risky if the parent is going to return an exit status of zero. If the parent is going to return a non-zero exit status, then this approach can lead to quicker delivery into your mail drop.
^/etc/nmh/mts.conf~^nmh mts configuration file ^$HOME/.maildelivery~^The file controlling local delivery ^/etc/nmh/maildelivery~^Rather than the standard file ^/var/mail/$USER~^The default mail drop
`-noverbose' `-nosuppressdup' `-maildelivery' defaults to $HOME/.maildelivery `-mailbox' defaults to /var/mail/$USER `-file' defaults to stdin `-addr' defaults to the current user `-user' defaults to the current user
-addr and -user will be set the the user part of the Local-Mailbox profile entry, if set.
slocal was originally designed to be backward-compatible with the maildelivery facility provided by MMDF-II. Thus, the “.maildelivery” file syntax is somewhat limited. But slocal has been modified and extended, so that is it no longer compatible with MMDF-II.
In addition to an exit status of zero, the MMDF values RP_MOK (32) and RP_OK (9) mean that the message has been fully delivered. Any other non-zero exit status, including abnormal termination, is interpreted as the MMDF value RP_MECH (200), which means “use an alternate route” (deliver the message to the mail drop).
Only two return codes are meaningful, others should be.
slocal was originally designed to be backwards-compatible with the maildelivery functionality provided by MMDF-II.