Email remains in the delivery queue with the error code 451 4.4.2

Products

• Messaging Gateway

Issue/Introduction

Some emails remain in the delivery queue and show a 451 error code in the Control Center Message Queues view.

Symptoms
Emails remain in the delivery queue with an SMTP error code of one of, or similar to:

451 4.4.2 [internal] no banner
451 4.4.2 [internal] no BODY response
451 4.4.2 [internal] no RSET response
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

Cause

The Symantec Messaging Gateway (SMG) connects to the downstream server successfully, but does not receive a response. SMG considers this a successful connection with a transient failure in delivery and will continue to attempt to send to the problematic MX record.

Resolution

Workaround

1. Verify the destination MTA is not responding to the Messaging Gateway Appliance
2. Do one of the following:
   - Create a delivery domain record in the Control Center
   - Forward all outbound mail to another local mail server for external delivery

How to verify the target MTA is not responding to the Messaging Gateway Appliance

1. Perform an MX lookup for the domain.

   nslookup -type=mx example.com

2. Perform a telnet test connection to the SMTP port of the primary MX record IP address.
3. Verify that no response is returned.

To create a delivery Domain record for the working MX record IP address in the Control Center

1. Click on Protocols.
2. Click on Domains.
3. Click on Add.
4. Enter the recipient domain.
5. In the Acceptance tab, uncheck the "Local domain" tick box.
6. In the Delivery tab, check the "Optionally route this domain or email address" tick box.
7. Enter the "Destination host" IP address.
8. Click Save.

To forward all outbound mail to another relay that can deliver properly.

1. Click on Administration.
2. Under the Hosts section, click on Configuration.
3. Edit your Scanner(s).
4. Click on the SMTP tab.
5. In the Outbound Mail Settings section, select and configure "Relay non-local mail to" to point to the delivering relay.