Postfix in a multi-IP environment

If you have to install postfix in a multi-IP environment, say, if you need it to listen to two or more IP (for example a real IP and an alias on the same NIC), there is a cute directive in that let you decide which IP should postfix (well, it’s parts like smtp, virtual/maildrop etc) use when contacting an external server.

inet_interfaces =,, localhost
smtp_bind_address =

with inet_interfaces your postfix will listen to these 3 IPs, and with smtp_bind_address you will tell postfix to specifically use when contacting an external address.