Emails are stuck in the Symantec Messaging Gateway's (SMG) outbound queue with the messages "421 4.7.7 [internal] Unable to process message at this time".
Brightmail Engine Logs:
Error while attempting to resolve sender address: <SENDER'S EMAIL ADDRESS>.
DDS client: XML-RPC call returned fault 800206 - Attempt to authenticate to data source failed: <DDS SOURCE>
Directory Data Source:
-  800206 com.symantec.sms.dds.api.exception.DataAccessAuthenticationException: Attempt to authenticate to data source failed: <DDS SOURCE> at com.symantec.sms.dds.dao.SpringLDAP.ExceptionInspector.translateException(ExceptionInspector.java:147)
The SMG was unable to authenticate to the configured Directory Data Source (DDS) and was unable to resolve the sender's email address.
Verify that the DDS Administrator Credentials (Administration -> Settings -> Directory Integration ->