When delivering messages to the distribution lists larger than forty-thousand entries (40,000), the Symantec Messaging Gateway MTA may exit and restart.
When Messaging Gateway is configured to do distribution list expansion via the Administration -> Directory Integration page, the mail server creates duplicates of the original message in a process known as bifurcation. This is to allow group policies to be applied on a per recipient basis. For large distribution lists this process can cause the creation of a large number of entries in the message queue and increases memory utilization by the MTA process which can trigger a restart of the service.
This issue has been addressed with the SMG v10.0.2 release. Distribution list expansion and a number of other message handling processes have been optimized to prevent large distribution lists from destabilizing the MTA process.