Hi All,
Microsoft has received reports of an issue in which some customers that using Mac Outlook or Entourage may be unable to send messages exceeding a size of 6 megabytes. Engineers have identified the root cause of the issue and are in the process of a deploying an update to the affected environments. As a temporary workaround, the users can use Outlook Web App to send emails with large attachments. The next update will be provided by December 10, 2013, at 8:00 PM UTC.
Thanks,
Mindy Pan