[Dshield] open-source Exchange substitute

[Rick Leir]

Some projects exist, but I have not tried them.  Here is a partial list:
   http://www.open-xchange.com/
   http://www.OpenGroupware.org
   http://www.zimbra.com/
A comparison:
http://www.siriusit.co.uk/index.php/documentation/email-calendaring/whitepaper-groupware

> The problem is that for all the flames Exchange takes from the security
> community, it *does* provide a lot of features that large sites often want to
> use, and those features are hard to find on other enterprise-ready open-source
> projects.