Answer
GMS has identified a message that has bounced from a remote system. The message is from a control account on the remote server therefore GMS will not deliver the email. Messages from control accounts are indicated as coming from a "NULL" address normally indicated by <>
In this case session Undefined was processing a message from a server at Undefined apparently from Undefined to Undefined.
If you wish to check the message that was bouncing, switch on the option in the configuration interface and check the /BadMes directory for the domain containing Undefined.
See Also:
Keywords:Bounce bouncing mail 8225