Comment FUD (Score 3, Informative) 183
This is to prevent spammers from being able to send mail from *.onmicrosoft.com. This is the online service, not to be confused with Office, the desktop app.
That cloud ought to be accessible by anybody's computer and through any sort of information sitting out on the Web.
As long as the server has the right crossdomain.xml file...
I've noticed several design suggestions in your code.