Communication (Mail Gateway concept) with MS Exchange

[Danny]

Greetings,

I am thinking of installing 4.9R, Postfix, and the latter I have yet to find to have
a FreeBSD server communicate as mail gateway with MS Exchange.

At this point, I do not want to point MX records to our Internet connection and
direct SMTP traffic into our LAN, for many obvious reasons, in addition to our
existing configuration - with our Internet email being hosted externally and
downloaded via POP3.

I would prefer to consolidate down to one (currently approx. 40 separate POP3 user
mailboxes for this one domain) catch-all POP3 mailbox at our email host, and then
have an app POP3 that mailbox down to a FreeBSD server, perform AV & SPAM
processing, then somehow deliver that mail to the appropriate user on the Exchange
server based on the headers of the email messages.

Anyone experienced, heard, or have any ideas?

Thank you,

- Danny