Amavis stopping

[Curtis NPC]

Postfix 2.1.0-3
Ubuntu LTS
Amavisd-new 2.10.1


Today suddenly mail just stopped being being delivered. I noticed the 
following errors:

(delivery temporarily suspended: conversation with 127.0.0.1[127.0.0.1] 
timed out while receiving the initial server greeting)

The mailq was of course backing up. Only by restarting amavis and the 
flushing the queue did mail get delivered.

Looking through the logs, I don't see any amavis errors. What is 
causing, what I assume is amavis clogging up?

Thanks!