edge transport server
Edge transport server is an Exchange Server 2010 role that helps route Internet email as well as protect the Exchange organization from viruses and spam.
Introduced in the Exchange Server 2007 release, the edge transport server role is deployed in an Exchange organization's perimeter network. Message protection and security are handled by various agents that run on the edge transport server and act on email messages as they are processed.
The edge transport server was discontinued as a server role in the Exchange Server 2013 release.