Not sure what you are looking for in an email system but for $7/month (per account) you can use Office365. Gives you the all the advantages of having your own Exchange server without any of the upkeep (spam filtering included, etc.) and of course allows for ActiveSync with mobile devices. I could even send you a trial (my business is microsoft certified partner).
Just thought I'd throw out the option as we've used it for a few clients and it works great