Collaboration Server

[gdecaires]

I'm looking for a complete collaboration / groupware solution for a four property business with 200+ users. We used to use exchange but have since moved to a Google / Postfix mixture for security, stability and cost reasons. That said, my users are sorely missing their shared contacts, calendars and task lists and I want to move my mail hosting in house again.
I've been toying with the idea of a postfix setup with multiple servers (power reliability issues make it smarter to have a server at each property) using routing rules. I've been looking and looking but haven't quite found what I need in a complete or at least small number of packages.
What I need is:

1) Mail hosted in-house with a server at each property though with a central point for incoming and outgoing email transport.
2) Single-sign-on service integration, perhaps with LDAP or MySQL.
3) Shared contacts, calendar and tasks.
4) Pricing options that make it more attractive than returning to Exchange.

If anyone can suggest a package or group of packages that would work together to provide this I would greatly appreciate it. Please post here or email me at gdecaires@eleganthotels.com

[jledhead]

Zimbra offers Open Source email server software and shared calendar for Linux and the Mac
open-xchange.com | now available in many languages

there used to be postpath that I would recommend above those, but its apparently been purchased by cisco
Scalix: Linux Email, Calendaring and Messaging Platform
Email and Groupware - easy to install, easy to use. - Citadel.org
OpenGroupware.org
Gordano Messaging Suite (GMS) - Collaboration and eMail server software

some free and some not.