I have a dual-homed mail server, so it have IP1 and IP2 on it. I set it up so it answers on both IPs while send via single link only.
The only thing I miss is how to figure out (and log it) which interface given connection comes to? It is for statistics mostly but I'd like to know which incoming interface is used for message to send it or by IMAP/POP session.
In Exim I can log IP of interface that received the message, but in Postfix can't find any. Frankly it won't say much in logs at all, and I think I need some trick to allow it.