[horde] Recomended Windows Mail Server

[Mikal & Suzi Romein]

Gidday

Just wondering what the consensus is on  good mail server for windows, 
preferably open source. I have exchange server on windows server 2003, but 
would like an alternative if possible. I have tried hMailServer but I cannot 
find any facilities to have shared mail folders, and I really need this 
feature. hMailSever is great except for this, maybe I am overlooking the 
feature somewhere.

Mikal