After Microsoft Exchange 2010 RollUp 8 is installed, Microsoft Exchange Transport service failed to load until SMSMSE is uninstalled. Hence SMSMSE transport agents were removed from Exchange Transport Agents
.
When SMSMSE is being reinstalled, installer will fail to install SMSMSE transport agents. The agents cannot even be installed manually by following this document -
How to manually install Symantec Mail Security for Microsoft Exchange (SMSMSE) transport agents.
Error shown under Exchange PowerShell while installing the agents manually -
The TransportAgentFactory type "Symantec.MailSecurity.Server.TransportAgent.SMSMSERoutingAgentFactory"
doesn't exist. The TransportAgentFactory type must be the Microsoft .NET class type of the tranport agent factory.