Email server suggestion?

Hello All,

With the end of support for Windows Server 2003, it's time for me to finally 
upgrade the mail front-end that we use for MHonArc. (currently using IMail 8.X).

What are folks using these days as their mail server for MHonArc?  I would like 
to move all the way to Server 2012R2 if possible.

Any suggestions would be greatly appreciated!

-Dave