In Symantec Messaging Gateway (SMG), most valid incoming messages are shown as "Abort" in the message audit log. After further investigation there are DDS errors found in the Logs and the problem does not seems to be related to a Firewall or SMTP filtering upstream from the SMG.
com.symantec.sms.dds.api.exception.DataAccessAuthenticationException: Attempt to authenticate to data source failed: testLogin() failed due to incorrect credentials
 Error while attempting to resolve recipient address: [email protected]
The account or password used to save the Directory Integration (DI) source has most likely expired and Recipient Validation cannot work. Valid messages are rejected on the SMTP level with the incorrect verdict since the DI source is not accessible.
1. In the Directory Integration source - Recipient Validation - enter a valid email address, preferably a service account with a non-expiring password
2. Save the settings to update the DI source
3. Restart the MTA in Administration - Configuration - edit host - Services - MTA Stop/Start
4. Wait about 5 minutes and monitor the message audit log to confirm mails are now being validated correctly and delivered normally
Symantec Messaging Gateway 9.x