Need a POP, IMAP, or web front for Exchange Server

I want to put a POP or IMAP or web front-end mail
server (actually all 3, if possible) in my
company's DMZ, with access from the Internet. I
have Exchange 5.5 inside (and would love to get
rid of it but am not allowed to at this point). I
have to keep all the mailboxes on the Exchange
server. I don't trust putting an Exchange server
out where Internet users attach to it directly -
certainly not using OWA/IIS, at least. And the
big shots don't want to spend $ for another
Exchange server anyway. (Maybe if they like the
new front end, they'll let me get rid of
Exchange!) Anyway, does anyone know of a product
out there (preferably open source) that can act
as this kind of front end for these Exchange
mailboxes?

Thanks...Scott



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