Did the evaluation ..
Every year we look at the main email hosting services and we're still cheaper fully loaded compared to any of the cloud solutions as well we'd have to forgo much of the customization we have done to our email environment.
It makes sense if all you do is email and basic email usage. Beyond that most providers have hard settings that apply to everyone. They actually told us we should do a hybrid model (cloud and on site -- umm that's going to cost us MORE money!?!)
We did a lengthy discovery with Microsoft and I've sure other enterprises have done the same exercise and they basically told us they can't beat our in house cost or provide half the ways we use email. And forget it if you use public folders, Microsoft acts like no one uses them.
Cloud is getting there but until you have full control of the email servers it's all setup for scale and lowest cost model (that favours the cloud not you).
