After installing Symantec Mail Security for Microsoft Exchange (SMSMSE) 6.x on an Exchange 2007 server and enabling Premium AntiSpam there is a significant impact on mail flow.
This problem occurs when all of the following are installed or enabled on the Exchange 2007 server:
Client Access Role
Hub Transport Role
Symantec Premium AntiSpam
The event log contains the following entry:
Source: MSExchange Extensibility
Description: The execution time of agent 'SMSMSESMTPAgent' exceeded 300000 (milliseconds) while handling event 'OnEndOfData'. This is an unusual amount of time for an agent to process a single event. However, Transport will continue processing this message.