I've worked as a sysadmin for some years and what I keep coming back to is that users like Microsoft Outlook and want to use its Exchange features. I have tried my fair share of commercial alternatives but usually there is either a fundamental feature missing or there are stability issues.
In short I am looking for a Microsoft Exchange Alternative with the following features:
- Authentication through SQL or LDAP
- Has a solid, comfortable web interface for the users when they are off-site
- Supports replication and load balancing (if one fails, the second one should be already running)
- Outlook client support (or a really good alternative client)
- Resource booking (meeting rooms, projectors, company jet, etc)
- Calendar (shared/private) and Email (if that wasn't obvious)
- (Optional) A cross-platform client for us *nix users.
- (Optional) Corporate support contracts available
- (Optional) An open-source software is a plus
Please keep your answers as detailed as possible to determine that you've successfully deployed the software and it fulfills the needs. If I wanted a list of claimed alternatives , I would simply Google it.
I've personally tried Binary Server, Novell Groupwise, homegrown Postfix/Cyrus stuff and in the end the 'real thing' because those users just love Exchange.
Please help me find a good alternative.