Postfix smtp_fallback_relay issues
 

Hi guys, I am having an issue with Postfix and hope members can help. We have been looking for ways to send external mail to a secondary smart host if our primary exchange server goes down. Ex: Transport file:

mailtest.example.com smtp:[192.168.99.99]

If mailtest goes down we need to find a new host to relay to. So I discovered the smtp_fallback_relay directive which is perfect and does the job we were looking for by allowing us to define:

smtp_fallback_relay = [192.168.99.100]

However we are seeing issues were mail from internal hosts from exchange destined towards external unreachable mail servers are also getting relayed back to our smtp_fallback_relay. Ex: I send message to someone@nonexistent.domain and the server rejects the message it will come back to our exchange host. How do I only use the smtp_fallback_relay for inbound mail messages only and exclude outbound mail from the exchange servers from using the fallback directive?

Thanks

2 Server Instances?
 

Exchange? YUK!

The only way I can think of to accomplish what I think you want to do is to use 2 instances of Postfix. One to process incoming mail on port 25 and another instance running on a different port say 2525 for outgoing mail from Exchange. This will of course mean you will have to direct Exchange to forward outgoing mail to port 2525 of your Postfix box. I think that will accomplish what you want.

Another option might be to have Exchange forward outgoing mail to your ISP's Mail Server.

Maybe someone else will have a better solution.