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mh-alias - format of nmh email-address alias files


Each line of an nmh alias file takes one of the following forms:

alias : address-group

alias ; address-group

< alias-file

; | : | # comment


address-group	:= address-list
			|  < file
address-list	:= address
			|  address-list, address

Continuation lines end with “\” followed by a newline character. This also applies to comment lines. Thus, the line following a “\”-terminated comment line is a continuation of that comment line.

Alias-file and file are Unix file names. Alias file contents are case-insensitive, with the exception of filesystem path names.

If the line starts with a “<”, the file named after the “<” is read for more alias definitions. The reading is done recursively, so a “<” may occur in the beginning of an alias file with the expected results.

If the address-group starts with a “<”, the file named after the “<” is read and its contents are added to the address-list for the alias.

In match, a trailing “*” on an alias will match just about anything appropriate.

An approximation of the way aliases are resolved at posting time is:

Build a list of all addresses from the message to be delivered, eliminating duplicate addresses.
For those addresses in the message that have no host specified, perform alias resolution.
For each line in the alias file, compare “alias” against all of the existing addresses. If a match, remove the matched “alias” from the address list, and add each new address in the address-group to the address list if it is not already on the list. The alias itself is not usually output, rather the address-group that the alias maps to is output instead. If “alias” is terminated with a “;” instead of a “:”, then both the “alias” and the address are output in the correct format (with the alias quoted if necessary and the address wrapped in <>).

Since the mh-alias file is read line by line, forward references work, but backward references are not recognized.

Example Alias File

sgroup: fred, fear, freida
fred: frated@UCI.example
b-people: Blind List: bill, betty
Unix-committee: <unix.aliases
news.*: news

The first line says that more aliases should immediately be read from the file /etc/nmh/BBoardAliases. Next, “sgroup” is defined as an alias for three names, and one of them, “fred”, is a forward reference to another alias for “frated@UCI.example”.

The alias “b-people” is a blind list which includes the addresses “bill” and “betty”; the message will be delivered to those addresses, but the message header will show only “Blind List: ;” (not the addresses). The alias must not be terminated with, or contain, a semicolon. Note that blind lists are not supported with the sendmail/pipe mail transport method.

The definition of “Unix-committee” is given by reading the file unix.aliases in the user's nmh directory.

Lastly, “news.anything” is aliased to “news”; the full stop is just another literal character.


Default alias file.


System-wide default alias file.


ali(1), send(1), whom(1), getgrent(3), getpwent(3), post(8)


Although the forward-referencing semantics of mh-alias files prevent recursion, the alias-file directive may defeat this. Since the number of file descriptors is finite, such infinite recursion will terminate with a meaningless diagnostic when all the fds are used up.

Earlier versions of this man page showed a semicolon at the end of the blind list example. That caused the preceding alias to not be expanded. There must not be a semicolon at the end of, or within, the address group of a blind list. post will append the semicolon to the blind list name.

2014-04-18 nmh-1.8-RC2