Some emails get stuck in the delivery queue of the latest version of Symantec Messaging Gateway (SMG) despite presence of responsive MX records for the destination domains.

The stuck emails in the delivery queue show one of more of the following reasons for delivery failure:

451 4.4.2 [internal] no HELO/EHLO response
451 4.4.2 [internal] no MAIL FROM response
451 4.4.2 [internal] no RCPT TO response
451 4.4.2 [internal] no DATA response
451 4.4.2 [internal] no BODY response

When attempting to deliver a message to the destination mail server, the destination server stopped responding at some point in the SMTP protocol conversation. The point at which the destination server stopped responding is reflected in the queue status message.

This issue is mostly due to a non-responsive host serving as the primary MX record of destination domain, it is best to contact the administrator of the destination domain to fix the non-responsive host.  In the event this is not possible, use the "Destination Routing" option on Protocols > Domains page to configure a responsive host for the destination domain to which the mail can be delivered successfully.

• 451 4.4.2 [internal] no HELO/EHLO response