I am using a MAC with Outlook 2011 against the new outlook.com (preview) version that is like an exchange server.  I have two MAC computers that starting failing to send a message to my outlook.com account. Both are fully upgraded and patched as of 9/13/2015.

The error is "Invalid MIME content." and the message is moved to my drafts folder with Error Code - 19789

Again this is on two systems. I deleted all contacts from the outlook account. And I still the same error on both systems.

This is something on the server side and most likely because of the migration from the old "outlook.com" to the new (preview) version of "outlook.com".

Need help with this.