Exchange replacement

[Hans du Plooy <hansdp-lists@sagacit.com>]

Hi,

I've given up on trying to get a decent free OSS replacement for 
Exchange - it's simply not worth the time and effort for the avarage SME.

What I am looking for is something that can do shared calendering and 
contacts, that Outlook can plug into - without a plugin.  If I can get 
that, I can actually drop exchange, give the guys imap or pop with pst 
files sitting on the server.  And use postfix - that would be the 
happiest day of my life...

Anybody know of such a beast?

Thanks
Hans