Symantec Messaging Gateway (SMG) cannot deliver some or most email messages.
Emails stay in the delivery queue with the message "450 4.4.1 [internal] Connection Timed Out"
This error indicates either that the connection is timing out, or is being interrupted while the message is being transferred to its destination. This can be a local or non-local error.
If you have a firewall between SMG and the destination SMTP server—which can be a local or non-local mailbox server—ensure that SMTP and ESMTP features are disabled. Consult with your firewall vendor to learn how to disable these features.
Firewalls that are known to have such features include:
Cisco ASA - Disable all esmtp_inspect features
Cisco Pix - Disable Mailguard
Checkpoint - Disable the SmartDefense technology for SMTP/ESMTP