Alias support

Courier's support for the address alias file is similar to sendmail's, but with some notable differences.  Aliasing addresses to programs is not allowed, the alias list is strictly a list of E-mail addresses. Mail addressed to a name of the alias is delivered to the list of E-mail addresses defined for that alias.  The name of an alias has no corresponding mailbox, with one exception. The alias may include an E-mail address that is the same as the alias name, in which case the mail gets delivered to this mailbox in addition to being sent to all the other addresses defined for that alias. Otherwise, if a mailbox with the same name as an alias exists, it will not receive any mail, as any mail addressed to it will be forwarded to the alias members instead.

The alias file is called aliases.dat. Courier looks for aliases.dat first in the ${COURIER_HOME}/$ARCH/lib/modules/MODULE directory. If not found, Courier looks for aliases.dat in ${COURIER_HOME}/lib. This lets you define aliases that can be mailed to only locally, or define system wide aliases.

Please note that if lib/modules/MODULE/aliases.dat exists, and the E-mail address is not found there, Courier wll try again using lib/aliases.dat.

makealiases

The aliases.dat file is created using the makealiases program. The syntax makealiases is as follows: 
   makealiases -src=srcfile -tmp=tmpfile -auxtmp=auxtmpfile \
      [ -alias=aliasfile ] [-dump] [module]
The src, tmp, and auxtmp parameters must be specified. Either the alias parameter or the dump flag must be specified.

srcfile is a text file with alias definitions. makealiases uses two temporary files to create the aliases.dat file. You must specify the names of those files using the tmp and auxtmp parameters. aliasfile is the complete pathname to the final aliases.dat file, which should be either in the lib directory, or in the MODULE directory. tmpfile and auxtmpfile must be on the same filesystem as aliasfile.

You may not have more than one instance of makealiases running at the same time, using the same temporary files. makealiases automatically removes the temporary files when done.

It is safe to run makealiases while Courier is running. The new aliases.dat file takes effect immediately.

All E-mail addresses in srcfile are rewritten to the canonical format. The optional module parameter specifies the module whose rewriting functions are used. If not specified, it defaults to local, so that you can specify addresses in srcfile without your local domain name.

The -dump flag prevents the alias file from being created. Instead, makealiases just rewrites all the addresses, removes the duplicates, and displays the final alias list on standard output.

srcfile can be set to "-". makealiases will read alias specifications from standard input.

The alias specifications file.

Blank lines in the file are ignored. Comments may be present on lines that start with the # character, which are also ignored.

An alias specification takes the form of:

alias: address1, address2, address3 ...

This specifies an alias whose name is alias. Mail that's sent to alias will be delivered to the specified list of addresses instead.

Instead of specifying an address, another alias can be used in its place, inserting the contents of the second alias list into the first alias list.

An alias specification may use mutiple lines. Start the second line with a tab character, or a space. For example:

everyone: john, steve, mary, alice, tom,
          harry, gene
For example, here's a three person organization. Gloria is in Sales, Steve is a system administrator, John does both sales and system administrators: 
sales: john, gloria
 
sysadmin: steve, john
 
everyone: sales, sysadmin
This alias file specifies that mail addressed to 'sales', will be delivered to the john and gloria accounts. Mail sent to 'sysadmin' will be delivered to to the steve and john accounts. Mail sent to 'everyone' will be delievered to steve, john, and gloria. Although john is listed twice in the everyone alias - once in the sales alias, and the second time in the sysadmin alias - john will receive only one copy of the message. The makealiases command (and the submit command also), automatically eliminates duplicates. Running makealiases with the -dump flag results in the following output. 
everyone@example.com: john@example.com, gloria@example.com, steve@example.com

sysadmin@example.com: steve@example.com, john@example.com

sales@example.com: john@example.com, gloria@example.com
In this example, the local domain is '@example.com'. The makealiases commands automatically converts all addresses to the canonical format.

The company grows in size, and it is now necessary for someone to be available 24 hours a day. Steve volunteers, and the following change is made:

sales: john, gloria
 
sysadmin: steve, john
 
everyone: sales, sysadmin
 
steve: steve, steve@domain.com
All mail sent to steve will now have a second copy mailed to steve@domain.com, IN ADDITION to being delivered to the local mailbox. steve@domain.com is Steve's Internet account at home. This changes affects all mail sent to steve, not just to mail sent to one of the defined aliases. Running makealiases with -dump now results in the following output: 
everyone@example.com: john@example.com, gloria@example.com, steve@example.com,
        steve@domain.com
 
steve@example.com: steve@example.com, steve@domain.com
 
sysadmin@example.com: steve@example.com, john@example.com, steve@domain.com
 
sales@example.com: john@example.com, gloria@example.com
This kind of forwarding should really be implemented in the .courier delivery specification file in Steve's account. Although allowed, aliases should never have the same name as a local account. Typically, you should define aliases for postmaster, and mailer-daemon.

The  -dump flag

The previous examples of -dump flag's output give an indication of what makealiases does:

The aliases.dat file

The aliases.dat file is a GDBM (or a DB) database. Unless the list of addresses in a single alias is large, the layout is pretty basic. The GDBM/DB database is keyed by the alias name, and the contents of the record are the addresses defined by the alias. Each address is followed by a newline character.

In order to prevent the GDBM/DB library from consuming excessive amounts of memory, if an alias defines a large list of addresses, the list is saved in multiple records. The key of the second record is the alias name, followed by a newline, followed by "1". If a third record is necessary, it's name is the alias name, followed by a newline, followed by a "2". And so on.

Differences from sendmail's /etc/aliases file

Although Courier's implementation of aliases.dat may seem very similar to sendmail's /etc/aliases file, there are some important differences: