On my new dedicated server, I’ve been getting reports of mail bounces. Looking more closely at them, I found they said “451: Deferred sender callout cannot be verified.”

This is the result of an anti-spam measure that Cpanel enables by default for Exim. It took a while, but I finally found the well-written discussion and fix on Michael Brandonisio’s blog.

Basically, you simply add a white-list to exim for people who have misbehaving ISPs. The problem is really on their side, but telling them to fix their mailservers just doesn’t seem to work very well.

[tags]exim,cpanel[/tags]