A

MS Exchange keeps breaking, Apple, Android and everyone else take one for the team and take the blame: http://support.apple.com/kb/TS3398

All the discussion is about portable devices "not working" even though it is MS Exchange that quits. They should all just get over it, that's what MS Exchange does, it breaks. Eventually they should just learn to shut up and take what Bill has to give them, either by getting used to the fact that they will never get much done tethered to Bill's Exchange, or by being harassed and brow beat by the Microsoft Insiders for 'making them look bad'

http://www.kolab.org/ http://www.citadel.org/ http://www.opengroupware.org/

The late, great Zimbra should also get a mention because it is now part of Microsoft's Yahoo. Ostensibly one of the goals of the hostile take over was to crush Free and Open Source Software developer teams like the one on Zimbra.

There are also calendar servers which integrate well with other systems. Any web designer worth his coffee grounds can hook them together with the mail service:

http://www.bedework.org/ http://andrew.triumf.ca/dingo http://trac.calendarserver.org/

If plain old mail is what you need, then look no further than these:

http://www.dovecot.org/ http://www.postfix.org/ http://www.exim.org/

If lusers miss some of the traditional features of MS Exchange such as downtime, unreliable connections, lost mail and delayed mail, there are many work-arounds.

* Downtime can be simulated by blocking the mail ports with the firewall for a few minutes every hours. MS Exchange monkeys usually have the Windows box underneath reboot every hour, to help hid instability this takes ten minutes or so each hour.

* Unreliable connections can be simulated by having the firewall drop random packets to or from the mail service. Be sure to just drop the packets, a return will send an icmp message to let the client know and that would not be as slow.

* Lost mail can be configured into the spam filter. Just have it delete 10% - 33% of incoming and outgoing mail. 10% used to be the industry average for MS Exchange but in many deployments that loss has been improved to 20% or even 30%!

* Delayed mail can also be simulated by the firewall or by the spam filter. Just bounce the message back using the spam filter or use the firewall to temporarily block incoming messages.

That way even if you use functional software and leave MS behind, you can still experience the chaos and accusations found in MS shops. A cold-turkey move might be too much for some fragile minds and an occasional round of "didn't you get the memo?" ought to keep them in familiar territory during the phaseout.