I run my own domain off a dynamic IP but all my postfix uses relayhost set to smtp.myisp. This works 99.9% of the time but I have encountered two recipients who use Barracuda's that block email from my domain.
The bounce includes "(reason: 554 Service unavailable; Client host [smtp.myisp] blocked using Barracuda Reputation; http://bbl.barracudacentral.com/q.cgi?ip=mydomainIP)". The Barracuda is looking at the sender IP (mydomainIP) instead of the relayhost IP. Is there another way to run a mailserver? Is there a standard I can read?
