NAME

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

DESCRIPTION

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

alias : address-group

alias ; address-group

< alias-file

; | : | # comment

where:

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:

1): Build a list of all addresses from the message to be delivered, eliminating duplicate addresses.
2): For those addresses in the message that have no host specified, perform alias resolution.
3): 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

</usr/local/etc/nmh/BBoardAliases
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 /usr/local/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.

PROFILE COMPONENTS

Aliasfile:: Default alias file.

FILES

/usr/local/etc/nmh/MailAliases: System-wide default alias file.

BUGS

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.