Hi,
we are using two external MX servers in separate data centers. Both of them are running postfix since many years without problems.
Internally we do have a postfix server as final destination for all domains. On each MX we have defined a relay_transport with specific settings that relay mail to our internal server. For this we use transport:[A RECORD]:port as relay_transport.
Now we have two links to our internal server and we observed that it was the right decision to have those two links. Our internal server got two IP addresses (one per link) and is listening on both of them for connections from the MX servers. But we have no clue how to set up a secondary relay_transport that kicks in if the primary is offline. So, currently we cannot use the backup link for incoming mails. We can only specify one relay_transport entry, means one IP address, with a transport.
Maybe smtp_fallback_relay would be a solution but we are unsure. smtp_fallback_relay got the problem that it seems to use the smtp transport only, and then we are unable to set all the transport stuff that we need (header manipulation, certificates, filters, etc).
We also thought that we could use transport:MX RECORD:port and give them different prios using DNS but in our special case this is not possible.
What is the right way to define a secondary relay_transport that kicks in if the primary is down and switches back to the primary if it comes up again? (We would like to change as few as possible because this is a pretty well running system.)
I thank the community for tips, hints and help!
Cheers!
-lutzn
