Replacing Microsoft Exchange

[Thomas Cameron]

IMHO, Exchange is Microsoft's killer app for a number of reasons.  I am
about to go do an Exchange 2003 installation for a client because the
president of the company likes the fact that he can sync his mail on his
laptop while he is on the road, because he can schedule meetings through
Outlook, he can check his mail through a web based application (OWA) and
his staff can sync their schedules with a variety of handhelds.

I can counter most of his arguments piecemeal, but I really can't point
to a single F/OSS solution, or even a suite of F/OSS solutions which can
beat Exchange's features.

So here is my question - has anyone had any success in replacing many or
all of Exchange's features with any F/OSS solutions?

It would be really cool if there were a F/OSS plugin that allowed
Outlook 2000 to use a F/OSS backend like IMAP and LDAP or something like
that.  I have seen some commercial products like Toltec Connector and
Bynari, but I am really interested in F/OSS.

Thanks,
Thomas Cameron, RHCE, CNE, MCSE, MCT