I've been using Exchange4Linux for the past year and a bit now with moderate success, but they've discontinued E4L development and joined up with the Zarafa folks.
As we were Exchange4Linux, all of our users were running Outlook of various versions (2000 and 2003). We have a very large (6000+) shared contacts database and are using most of the features that Outlook+Exchange provide (shared folders, tasks, journals, calendars, delegation, etc.). We use E4L because it was the *only* server-side solution that didn't give Outlook the screaming heebie-jeebies.
Since I'm going to be moving away from E4L anyway, I am taking the time to evaluate alternatives as well. Zarafa's pretty much an Outlook-only solution, much like E4L was, and it uses MySQL as Zimbra does.
Since almost all of my users will be using Outlook (moving to Outlook 2007), what can I expect from Zimbra Network Professional edition in terms of what does and does NOT work properly from an Outlook standpoint?
Also, I can see the various open-source products that compose the backend of Zimbra, but several threads in the Administration and Installation forums say that Zimbra requires the "Zimbra-specific" versions -- where are the patches/changes to the OSS versions? Do I have the complete source for the Zimbra backend available to me? What's proprietary? Can I download the source tarball for the NP edition and build a complete product? What about the Outlook connector?
I've also noticed some topic posts where "routine" problems such as running out of disk space ended up in a completely corrupted datastore that had to be restored from backup (January 2007) -- are there any other known "gotchas" I can expect? (If I can expect them, I can prepare for them -- in the case of this particular one having disk space notification would help).
With regard to the system it runs on -- I see RH is the officially supported platform, but others are able to work. What is absolutely required from the distribution? I tend to use Slackware and don't expect distribution-level support, but are there any gotchas lurking for me in terms of required infrastructure (PAM, glibc-specifics, etc.)?
The architecture of Zimbra suggests that it could very well be DB-agnostic one day. Is Zimbra intentionally using any MySQL-isms (INSERT "*", etc.) which would prevent this, or is it simply a matter of finding out where the inconsistencies are and working on them? As an administrator not afraid of getting his hands dirty, do I have any capability to fix these issues as I find them in NP? How is the DB layer abstracted, do I need to recompile the application or is there a "translation" file which is used to select the appropriate SQL statement?
Overall, Zimbra looks very good. However, I've been at this game long enough to know that it's easy to look very good, which is why I've been scouring the forums to see how well it really works. :-)