[nflug] Postfix & Virtual DOmains

[Wolfe, Robert]

I know a lot of you may know this already but I didnt until this morning :)  So, since I found this tidbit of information to be quite useful (since I do email hosting) I thought I would pass this along:

Date: Wed, 05 Mar 2003 12:11:10 +1100
From: Tom Ryan tom.ryan at whitehorsestrategic.com
Subject: RE: multiple domains with postfix
To: luv at luv.asn.au

Adam Clarke wrote:
> Theng Ung wrote:
> >I am new to postfix. I manage to get it going with two
> >domains. The problem is though if I send an email to
> >user1 at domain1 or user1 at domain2 it arrive at user1
> >mailbox.
>
> I'm afraid that's how it works. What you need to do is give each user a
> different local account and direct their domain specific mail there.
>
> So user1 at domain1 might have an account of user1_d1 (or the like) and
> user1 at domain2 might be user1_d2.

Incorrect. You need to use virtual domains. Virtual domains take
precedence over local aliases. Having a local account or alias of the same
name does not interfere with a virtual mapping.

The process is simple. Here is what you need to do:

0. read this whole email before you start ;)

1. main.cf additions
1a. run "postconf -n" and check that there is a line like:
virtual_maps = hash:/etc/postfix/virtual
if not add that line to main.cf
1b. check that all the domains for which you will receive
mail are referenced in $mydestination in main.cf

2. the virtual table
2a. add your virtual aliases to the virtual_maps from main.cf
in your case use this format:
user at virtual.domain localuser0
user at other.domain localuser1
NOTE: do NOT include a line like:
virtual.domain ANYTHING
or you will no longer receive mail to local users not
mentioned in the virtual file. If you read up on this
you'll understand why. if you don't... just go along
with me on this one, and it'll work. ;)

3. use the changes
3a. restart postfix:
$ postfix reload
3b. generate the virtual table hash:
$ postmap /etc/postfix/virtual
(or wherever your virtual file is)

NOTES:

the "virtual" equiv of newaliases:
$ postmap /etc/postfix/virtual
run that when you update the virtual table.

here's a more complete look at the ways you can map addresses:

----from the openbsd postfix package's virtual(5) man page-----
user at domain address, address, ...
Mail for user at domain is redirected to address.
This form has the highest precedence.

user address, address, ...
Mail for user at site is redirected to address when
site is equal to $myorigin, when site is listed in
$mydestination, or when it is listed in
$inet_interfaces.

This functionality overlaps with functionality of
the local alias(5) database. The difference is that
virtual mapping can be applied to non-local
addresses.

@domain address, address, ...
Mail for any user in domain is redirected to
address. This form has the lowest precedence.

In all the above forms, when address has the form @other-
domain, the result is the same user in otherdomain. This
works for the first address in the expansion only.
--------------------------------------


And that's all the postfix that's fit to print ;)

regards,
tom ryan.