If you are seeing the following error, on messages in the Symantec Messaging Gateway queue: 450 4.4.1 [internal] Connection Timed Out
These messages are being interrupted during transmission. This leads to the sender receiving a delayed delivery notice. This is caused by something in the message being rejected by the Cisco router during inspection of the traffic. To fix this you must disable all esmtp_inspect features on the ASA:
On the Cisco ASA local to the Symantec Gateway:Configure>Firewall>Service Policy Rules>Open Inspection_default>Rule Actions[Tab]>Deselect ESMTP