Mail/collaboration server

[Bradley Alexander <storm@tux.org>]

I've been using Kolab for my mail/collaboration software for home about
4 years. Right now, the hard drive on the machine I'm running on is
failing. I have other hardware on which to run the new mail server,
however, I am trying to decide the best suite to use. I can stick with
Kolab, as there is a new release, however the installation is kind of
clunky on Debian (basically installing RPMs). The main features I am
looking for, in order of priority:

* Good-to-excellent antispam (bayesian filter, spamassassin, but extensible)

* Shared calendaring with Palm integration

* Preferably opensource and cost free

* (preferably) Postfix-based

Now kolab has been falling down on the anti-spam job, but part of this
may be because of the failing drive.

I see myself having the following options.

1. Stick with Kolab on the new server.
2. Scalix
3. Zimbra
4. Hula

>From what I have read in my initial perusal, Zimbra and Scalix, while
commercial, both have free/community versions. I'm looking at less than
a dozen accounts, and most will be accessed by Linux (kde, gnome or
enlightement). Zimbra seems fairly mature. Hula would also be a
consideration, however, their documentation on antispam is almost
non-existent, and the sections that do have information generally have
"Coming soon..."

Does anyone have experience deploying any of these servers? How painful
is migration of existing mail stores to the other systems? Am I missing
any possibilities?

Thanks,
--b