Disable or bypass Antivirus on some Message

[thorng]

Recently, one of our users try to send a message with .tar.gz attachments and triggering zip bomb detection. The file had unusually large compression ratio but it is still within reasonable size.

The problem is that I wasn't able to disable the scanning for this file even after looking around the amavisd.conf / amavisd.conf.in. I don't want to disable the Anti-Virus feature all together but I can I disable the certain archive types checking (.tgz for example)