This has now been fixed
Status: ServiceRestored
Last Update:
Dec 11 2013 7:09PM (GMT) Closure Summary: On Tuesday, December 03, 2013 at approximately 3:39 AM UTC, Microsoft received reports of an issue in which some customers using Mac Outlook or Entourage may have been unable to send messages exceeding a size of 6 megabytes. Microsoft engineers deployed an update across the affected environment which remediated impact. The issue was successfully fixed on Wednesday, December 11, 2013 at 5:00 PM UTC. A complete post-incident report will be available on the Service Health Dashboard within five business days.