postfix smtp_fallback_relay for deferred messages to a single domain

view full story

http://serverfault.com – I use Postfix to send messages to a mail server outside my organization which frequently rejects/defers my mail. My Postfix server sees that these messages are deferred and tries again, eventually getting through. Final delivery can take up to an hour, which makes my users unhappy. In comparison, mail from my Postfix server to other hosts works normally. I have now found out about a second, unofficial MX for this domain that does not reject/defer mail. This second MX does not appear when doing a DNS MX query for the domain. Therefore, for the problem domain I would like to use this second MX (HowTos)