Restrict which IP address listens on and sends mails

[Sven Luzar]

I found a very helpful feature from another github user:
https://github.com/dirtsimple/poste.io

• Restrict which IP addresses listens on mails
• Select which IP addresses sends mails

In combination with a pacemaker-controlled IP-Address it is possible to build a high available mail server. In the case of a hardware failure, the mail server can automatically switch to another server.

It would be great if you could add this feature to your mail server.