I'm trying to configure my postfix (2.9.6) mail server to initially try deliver messages directly to the recipient MX, then fall back to relaying through my ISP's mail server if it recieves a 5xx status code. My mail server is on the end of a home broadband connection so it falls foul of spamhaus filtering. I'm aware that I could relay everything through my ISP's server, but I'd rather not unless it is absolutely necessary. Call me paranoid.
I was hoping that something like this in main.cf would do the job (port 11125 is an stunnel to my ISP's mail relay, and does work if I set it as the relayhost)
relayhost = smtp_skip_5xx_greeting = yes smtp_fallback_relay = [127.0.0.1]:11125
That just bounces though, eg
Nov 19 12:46:15 mail-server postfix/smtp: E9275744: to=<email@example.com>, relay=mx2.hotmail.com[22.214.171.124]:25, delay=1.3, delays=0.04/0.01/0.46/0.81, dsn=5.0.0, status=bounced (host mx2.hotmail.com[126.96.36.199] said: 550 OU-002 (SNT0-MC1-F51) Unfortunately, messages from xx.xx.xx.xx weren't sent. Please contact your Internet service provider since part of their network is on our block list. You can also refer your provider to http://mail.live.com/mail/troubleshooting.aspx#errors. (in reply to end of DATA command))
So, is it possible to have postfix attempt to deliver via a fallback relay in the face of such a message?