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 firstname.lastname@example.org