...me and Zimbra, because as a fellow just posted, it's my butt on the line, as far as management is concerned, it was I who brought it home and whatever problems it comes along with... but it's gonna be fine :)
Long story short: picture some 5 NT4 servers with Netscape SuiteSpot just because it was an economic advantage around 1999 or 2000 (or so I was told). By 2003, with Windows OS migration and user demand growth, it just didn't fit anymore, and Exchange was on the table as an option, but management was hessitant due to $. Us sysadmins recommended Linux, because of performance, stability, etc. and management loved it because of $ (none, well, some.)
Consultant firm arrives and leaves us with just one server running OpenExchange (I think it was 'E' xchange by then) on Unified Linux 1.1 :S
5 years later, due to Windows OS migration and user demand growth, the SLOX frankenstein we ended up with couldn't keep up, downtimes here and there, and management puts Microsoft Exchange on the table, again, as pretty and economic as ever, with a helluva bargain from our partner channel (or so I was told).
My recommendation, Linux again :D
You'd think it was just as easy as going for the Linux leader (which undoubtedly is Zimbra hands down) just so long we wouldn't end up with Microsoft's, but boy was that one of the toughest recommendations I've worked in.
Scenario: 1500+ users, all of them using Microsoft Outlook 2003, 100 of them with a company-provided BlackBerry, 500 of them with some mobile gadget of their own and savvy-enough to sync it, a 10:1 ratio of Windows Server OS vs. Linux distro OS on servers... pretty much everything was hinting "Microsoft Exchange".
My stand, Zimbra can (I know I still need the BlackBerry Server, but so does Exchange) do BlackBerries, Outlook sync, Mobile gadgets (I love how "push" (IMAP4) works on my Sony Ericsson Z610), plus all the experience our staff has gathered in the past 7 years has been focused on Linux mail servers, we have a solid practice, there'd be some sort of learning curve, implementation time, and maturity process in adopting Exchange from zero, and, of course, Zimbra Open Source comes at the magnificent bling-bling of $0.
Next milestone: going Pro (NE). One step at a time guys :)
Awesome job people, I was thinking it was worth to point out that far from Open Source alone, an important force behind such a good product is the people working on it: one can tell, elegant solutions, not hacks, a strive for robustness, a liquid interface. I can tell guys, you've really thought about almost everything while building this. It's the kind of thoughtful engineering that sets the difference between an Audi and everything else, and that is felt the minute you grab the steering wheel. Serious congratulations to you all.
Awesome & welcome to the forums!