Sigh....
Gmail is fantastic if you don't want to pay, and yes, has ALOT of storage. There are cheap, reliable options out there. Exchange does not even feature cause you need to be Bill to afford it.
We host our own mail server. Cheap, easy to manage, reliable, backups and restore is a breeze (Epic fail for Exchange on restore!) spam rules pretty good (Gmail rules here!), web access, iDevice friendly plugs straight into Outlook (all recent versions) etc. etc. etc... as close to exchange as I could get!
Initial cost : R1,800-00 Incl – once off
Annual cost : R50-00 Incl / user.
Domain name Cost : R57-00 Incl / year (If you pay more, you are getting ripped off! - learn to do EFT's)
Current mail store : 100Gig
Sleepless nights : none
Total Cost : priceless!
Oh yes, Windows or Linux... and no, it is not postfix!