.\"	@(MHWARNING)
.\" @(#)$Id$
.SC MH-ALIAS 5
.NA
mh-alias \- alias file for MH message system
.SY
any \fIMH\fR command
.DE
This describes both \fIMH\fR personal alias files and
the (primary) alias file for mail delivery, the file

	@(MHETCPATH)/MailAliases

It does \fBnot\fR describe aliases files used by the message transport system.
Each line of the alias file has the format:

	alias : address\-group
.br
or
.br
	alias ; address\-group
.br
or
.br
	< alias\-file
.br
or
.br
	; comment
.br

where:

	address\-group  :=  address\-list
.br
		       |   \*(lq<\*(rq file
.br
		       |   \*(lq=\*(rq UNIX\-group
.br
		       |   \*(lq+\*(rq UNIX\-group
.br
		       |   \*(lq*\*(rq

.br
	address\-list   :=  address
.br
		       |   address\-list, address
.br

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 \fI/etc/group\fR.
An address is a \*(lqsimple\*(rq Internet\-style address.
Througout this file, case is ignored, except for alias\-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 \fI/etc/group\fR 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 \fI/etc/group\fR is consulted
to determine the group\-id of the UNIX\-group named after the `+'.
Each login name occurring in the \fI/etc/passwd\fR 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 \fI/etc/passwd\fR 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):

.in +.5i
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 resolution.

3) For each line in the alias file,
compare \*(lqalias\*(rq against all of the existing addresses.
If a match, remove the matched \*(lqalias\*(rq 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 \*(lqalias\*(rq is terminated with a `;' instead of a `:',
then both the \*(lqalias\*(rq and the address are output
in the correct format.
(This makes replies possible since \fIMH\fR aliases and
personal aliases are unknown to the mail transport system.)
.in -.5i

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

.ne 10
\fBExample:\fR
.nf
.in +.5i
<@(MHETCPATH)/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
.in -.5i
.fi

The first line says that more aliases should immediately be read from
the file \fI@(MHETCPATH)/BBoardAliases\fR.
Following this, \*(lqfred\*(rq is defined as an alias for
\*(lqfrated@UCI\*(rq,
and \*(lqsgroup\*(rq is defined as an alias for 
the three names \*(lqfrated@UCI\*(rq, \*(rqfear\*(rq, and \*(rqfreida\*(rq.
.sp
The alias \*(lqb-people\*(rq is a blind list which includes the
addresses \*(lqbill\*(rq and \*(lqbetty\*(rq; the message
will be delieved to those addresses, but the
message header will  show only \*(lqBlind List: ;\*(rq (not the addresses).
.sp
Next, the definition of \*(lqUNIX\-committee\*(rq is given by reading
the file \fIunix.aliases\fR in the users \fIMH\fR directory,
\*(lqstaff\*(rq is defined as all users who are listed as members of
the group \*(lqstaff\*(rq in the \fI/etc/group\fR file,
and \*(lqwheels\*(rq is defined as all users whose group\-id in
\fI/etc/passwd\fR is equivalent to the \*(lqwheel\*(rq group.
.sp
Finally, \*(lqeveryone\*(rq is defined as all users with a user\-id in
\fI/etc/passwd\fR greater than 200,
and all aliases of the form \*(lqnews.<anything>\*(rq are defined
to be \*(lqnews\*(rq.

The key thing to understand about aliasing in \fIMH\fR
is that aliases in \fIMH\fR 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 transport 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 \fBNOT\fR expanded into the headers of messages delivered.
.Hh
To use aliasing in \fIMH\fR quickly, do the following:

.in +.5i
First, in your \fI\&.mh\(ruprofile\fR,
choose a name for your alias file, say \*(lqaliases\*(rq,
and add the line:

.nf
.in +.5i
Aliasfile: aliases
.\" ali: \-alias aliases
.\" send: \-alias aliases
.\" whom: \-alias ailases
.in -.5i
.fi

Second, create the file \*(lqaliases\*(rq in your \fIMH\fR directory.

Third, start adding aliases to your \*(lqaliases\*(rq file as appropriate.
.in -.5i
.Fi
^@(MHETCPATH)/MailAliases~^Primary alias file
.Pr
^Aliasfile:~^For a default alias file
.Sa
ali(1), send(1), whom(1), group(5), passwd(5), conflict(8), post(8)
.De
None
.Co
None
.Hi
In previous releases of \fIMH\fR,
only a single, system\-wide mh\-alias file was supported.
@BEGIN: MMDFMTS
Now that \fIMH\fR uses \fIMMDF\fR as a transport system,
the system\-wide aliasing facility can be more consistently controlled by the
latter.
This means that at most sites,
the system\-wide mh\-alias file will be empty (or trivial at best).
@END: MMDFMTS
@BEGIN: MHMTS
This led to a number of problems,
since only mail\-system administrators were capable of (un)defining
aliases.
@END: MHMTS
@BEGIN: SENDMTS
This led to a number of problems,
since only mail\-system administrators were capable of (un)defining
aliases.
@END: SENDMTS
Hence,
the semantics of mh\-alias were extended to support personal alias files.
Users of \fIMH\fR no longer need to bother mail\-system administrators for
keeping information in the system\-wide alias file,
as each \fIMH\fR user can create/modify/remove aliases at will from any
number of personal files.
.Bu
Although the forward-referencing semantics of \fImh\-alias\fR files prevent
recursion, the \*(lq<\ alias\-file\*(rq command may defeat this.  Since the
number of file descriptors is finite (and very limited), such infinite
recursion will terminate with a meaningless diagnostic when all the fds are
used up.
.sp
Forward references do not work correctly inside blind lists.
.En