Email Server

In my post "New Email Server" I revealed a dilemma that I face every time I upgrade software that we have had for awhile. I want to go and look out at other solutions that would be better/cheaper before I do my upgrade. Well I have finally made a decision on the Email Server and we are sticking with MS Exchange.
Reasons:

1. We already have Software licensing for exchange
2. We desperately need to replace hardware and enterprise is enterprise as far as I'm concerned.
3. People do not like change and training is costly
4. We are currently an all-production MS shop and everything fits very well together now
5. There is the possibility of implementing Share Point and I would really like it to fit in with our mail solution.

I like to talk a big game but I really have to see an extreme value difference to actually move.