[exim] Is the Exchange 2007 Edge Transport Server required?

My employer is planning on migrating from Sendmail (Linux) to Exchange
2007. We also have an SMTP gateway server running the Exim 4 (Linux). This
gateway server also does spam filtering (Spamassassin) and virus blocking
(Clam-AV) and does it quite well.

As I understand it, the primary role of the Exchange 2007 edge transport
server is for spam and virus filtering and smtp gatewaying. Since these
roles are already being performed by the Exim server, do we really need a
separate edge transport server?


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Regards,
Conrad Lawes