Postfix Shared domains, UNIX system accounts

The simplest method to host an additional domain within postfix is to add the domain name to the domains listed in the Postfix mydestination configuration parameter, and to add the user names to the UNIX password file.

This approach makes no distinction between canonical and hosted domains. Each username can receive mail in every domain.

In the examples we will use "example.com" as the domain that is being hosted on the local Postfix machine.

 /etc/postfix/main.cf:
   mydestination = $myhostname localhost.$mydomain ... example.com

The limitations of this approach are:

• A total lack of separation: mail for info@my.host.name is delivered to the same UNIX system account as mail for info@example.com.
• With users in the UNIX password file, administration of large numbers of users becomes inconvenient.

The examples that follow provide solutions for both limitations.