I'm an admin who deals with a very large number of mail flow patterns. Everything from multiple versions of Domino to all incarnations of Exchange, all the major Unix flavors Postfix, Exim, Sendmail, Qmail as well as most major anti-spam vendors. I can say that most of the people I deal with who have switched to the Microsoft Cloud have been less than happy. Just an anecdote for you if you reconsider the switch.