Beware of header filtering, when sending to iCloud

It’s well documented that Apple/iCloud has a very obscure filtering policy. Emails are delivered to the server and then disappear.

After switching our mailserver, I ran into another problem that iCloud made all my emails disappear. After playing around with my recently added header checks in Postfix, I found that iCloud expects some of those headers to be present:


On the other hand, removing the internal IP is OK:


Hope this helps, if you run into the same problem.