We currently have approximately 50 users in an Exchange 2003 environment. We have about 25 users who get email via iPhone or other smart-phone. Currently, we are pushing the Exchange database cap (70 of 75 gig).
We are considering the pro version of Zimbra. Given this environment, what would you recommend?
Rather than give up and change your windows network to a Linux network becuase your nearly reaching the database limit. (thats how i took your question I appologies if i'm wrong) I wonder how much research you have done into see why your nearing the database limit?
I think for only 50 users to be using nearly 75GB of data, your either doing something wrong or users are sending/recieving massive emails whilst keeping them in their mailbox!
I think you will find it hard to find a linux based mirror of your Exchange solution, if not impossible (unless you excel in nix based OS)
If you have any questions let me know, I am happy to help you where I can.
UPDATE
I have just re-read your question, I assumed you are using SBS2003. Could you please confirm your Server OS?
If you are not using SBS2003 you should be able to add another mailbox store and migrate your heavy users over to it.
If you are still considering between Windows and Linux for 50 users ... I would suggest go for SBS (Small Business Server option bundled with a Dell Server) That will give you Exchange 2007 and will be very easy to manage.
Zimbra is good (Am not sure of the cost comparison between zimbra and exchange)
Your skills in Linux, Zimbra, SMTP, MTA etc will be the deciding factor here.
It's rather difficult to make suggestions without knowing a lot more about the context and constraints.
The way software is provided for Unix/Linux is usually quite different from the way Microsoft package solutions, particularly for messaging applications. Most people I know would build (have built) their own solution out of standard components e.g. postfix or sendmail for the MTA, various milters, ClamAv for virus checking etc, probably procmail for the MDA and courier or dovecot for the IMAP/POP server, squirrelmail for web access. (NB there are many other very good products which could be used in place of those I've mentioned).
However if you don't have strong Unix skills, then a pre-packaged commercial offering with a support package will often be a more cost-effective solution (Zimbra is exactly that - a bundle of free products and a bit of glue - you pay for the support - not for the software). The fact that you think of Zimbra and MSExchange as mail servers rather implies that you do not currently have the skills to build your own solution.
You could do a lot worse than Zimbra, but do have a look at Scalix and SME server
I've been running Zimbra Network Edition now for 2.5 years in a small business with about 50 mail boxes. It's not without it's warts but over all it's a very good solution and we've been happy with it.
Now that VMWare owns it they do offer it as a virtual appliance. But you can also install it on Ubuntu Server 8.04 LTS which is a free supported platform. Support for 10.04 LTS is currently marked as beta, what ever that means, but I would expect that will be a fully supported platform once Zimbra 6 is released.
But setting up a Linux system to run Zimbra isn't too difficult. The Zimbra installer contains all the pieces and their dependencies so the only think you really need to do at the Linux level is setup and secure SSH and if you wish setup iptables firewall to only allow the traffic you wish. You can use UFW if you're using Ubuntu.
Cost wise a 50 mailbox license of the Network Edition will run you $1500 a year.
