A customer updated the firmware from a Barracuda SPAM &Virus 300 firewall. The firmware was upgraded from version 3.4 to version 3.5.12.024. After the upgrade no email was coming in or going out through the Barracuda firewall.
All email was blocked and the following reason was visible in the message log:
Mail Protocol Violation
At first I couldn’t find a reason why all mail was blocked, so I contacted Barracuda and established a remote connection with Barracuda for remote troubleshooting. (I really like that feature). Finally the engineer found the problem. The Maximum Message Size value under Advanced – Email Protocol – SMTP Configuration was set to:
Yep, you read that correctly. I have no idea where that value came from. So I changed it back to the recommended value of 100 MB. After changing the value, mail started coming in and going out again through the Barracuda.