When your server was installed, we will have configured it to handle email for your primary domain. If you have any extra domains that you use, you can configure them as secondary domains in the Domains subsection of the Mail Server module.

When a secondary domain is configured, you can optionally set the system to automatically modify any emails it receives to that domain so that the recipient's address is changed to the primary domain. This is useful when the mail will be redirected to another mail server, as you only need to set that server up with the primary domain.