MH-ALIAS(5)							     [nmh-1.5]							       MH-ALIAS(5)

NAME

       mh-alias - alias file for nmh message system

SYNOPSIS

       any nmh command

DESCRIPTION

       This describes both nmh personal alias files and the global alias file for nmh mail delivery, the file

	    /etc/nmh/MailAliases

       It does not describe aliases files used by the message transport system.  Each line of the alias file has the format:

	    alias : address-group
       or
	    alias ; address-group
       or
	    < alias-file
       or
	    ; comment

       where:

	    address-group  := address-list
			   |  < file
			   |  = UNIX-group
			   |  + UNIX-group
			   |  *

	    address-list   := address
			   |  address-list, address

       Continuation lines in alias files end with `' followed by the newline character.

       "Alias-file"  and  "file"  are  UNIX  file names.  UNIX-group is a group name (or number) from /etc/group.  An address is a "simple" Inter-
       net-style address.  Througout this file, case is ignored, except for file names.

       If the line starts with a `<', then 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 `<', then the file named after the `<' is read and its contents are added to the address-list for the
       alias.

       If the address-group starts with an `=', then the file /etc/group is consulted for the UNIX-group named after the  `='.	 Each  login  name
       occurring as a member of the group is added to the address-list for the alias.

       In  contrast,  if  the  address-group  starts with a `+', then the file /etc/group is consulted to determine the group-id of the UNIX-group
       named after the `+'.  Each login name occurring in the /etc/passwd file whose  group-id	is  indicated  by  this  group	is  added  to  the
       address-list for the alias.

       If the address-group is simply `*', then the file /etc/passwd is consulted and all login names with a userid greater than some magic number
       (usually 200) are added to the address-list for the alias.

       In match, a trailing "*" on an alias will match just about anything appropriate.  (See example below.)

       An approximation of the way aliases are resolved at posting time is (it's not really done this way):

	 1) Build a list of all addresses from the message to be delivered, eliminating duplicate addresses.

	 2) If this draft originated on the local host, then for those addresses in the message that have no host specified, perform alias resolu-
	    tion.

	 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.  (This  makes  replies  possible	since  nmh
	    aliases and personal aliases are unknown to the mail transport system.)

       Since  the  alias  file is read line by line, forward references work, but backward references are not recognized, thus, there is no recur-
       sion.

       Example Alias File:

	    </etc/nmh/BBoardAliases
	    sgroup: fred, fear, freida
	    b-people: Blind List: bill, betty;
	    fred: frated@UCI
	    UNIX-committee: <unix.aliases
	    staff: =staff
	    wheels: +wheel
	    everyone: *
	    news.*: news

       The first line says that more aliases should immediately be read from the file /etc/nmh/BBoardAliases.  Following this, "fred"  is  defined
       as an alias for "frated@UCI", and "sgroup" is defined as an alias for the three names "frated@UCI", "fear", and "freida".

       The  alias "b-people" is a blind list which includes the addresses "bill" and "betty"; the message will be delieved to those addresses, but
       the message header will	show only "Blind List: ;" (not the addresses).

       Next, the definition of "UNIX-committee" is given by reading the file unix.aliases in the users nmh directory, "staff" is  defined  as  all
       users  who  are	listed	as  members  of  the  group "staff" in the /etc/group file, and "wheels" is defined as all users whose group-id in
       /etc/passwd is equivalent to the "wheel" group.

       Finally, "everyone" is defined as all users with a user-id in /etc/passwd greater than 200, and all aliases of the  form  "news.<anything>"
       are defined to be "news".

       The  key  thing	to  understand	about aliasing in nmh is that aliases in nmh alias files are expanded into the headers of messages posted.
       This aliasing occurs first, at posting time, without the knowledge of the message transport system.  In contrast, once the  message  trans-
       port  system  is  given a message to deliver to a list of addresses, for each address that appears to be local, a system-wide alias file is
       consulted.  These aliases are NOT expanded into the headers of messages delivered.

HELPFUL HINTS

       To use aliasing in nmh quickly, do the following:

	 1) In your .mh_profile, choose a name for your alias file, say "aliases", and add the line:

	      Aliasfile: aliases

	 2) Create the file "aliases" in your nmh directory.

	 3) Start adding aliases to your "aliases" file as appropriate.

FILES

       /etc/nmh/MailAliases	  global nmh alias file

PROFILE COMPONENTS

       Aliasfile:	    For a default alias file

SEE ALSO

       ali(1), send(1), whom(1), group(5), passwd(5), conflict(8), post(8)

CONTEXT

       None

BUGS

       Although the forward-referencing semantics of mh-alias files prevent recursion, the "< alias-file" command may defeat this.  Since the num-
       ber of file descriptors is finite (and very limited), such infinite recursion will terminate with a meaningless diagnostic when all the fds
       are used up.

       Forward references do not work correctly inside blind lists.

MH.6.8								   11 June 2012 						       MH-ALIAS(5)