Messaging Gateway (SMG) cannot deliver messages to some domains. Message Audit Logs indicate that messages are rejected with a 550 reponse code by the destination mail server and the message is discarded from the delivery queue.
"550 5.5.0 invalid ehlo/helo host.example.com" in message audit log.
Some mail servers perform DNS checks to validate the connection including the following:
Symantec recommends that when using SMG for outbound delivery the SMG hostname, A records, and PTR records all provide consistant identification for the SMG system.
When sending and receiving messages this is the name that Symantec Brightmail Gateway will use to greet other MTAs.
To change the MTA host name:
Once the changes are applied, retry the mail delivery:
As a best practice you should always match your external MX records with the MTA host name, for more information, please check the following article:
Symantec Messaging Gateway (SMG) - Best Practices: New Deployments
- The MTA host name on the Symantec Brightmail Gateway has a different name such as "smg.example.com"
- There are no public MX records with the MTA host name "smg.example.com"