Microsoft today released an update for Microsoft Office for Mac 2011



From MacRumors:

After installing the new Apple operating system, many Outlook 2011 users found themselves unable to access their mail due to a syncing issue that caused the app to hang whenever it attempted to access the server. Users were seeing a spinning Wait cursor whenever a sync was attempted and Outlook would become unresponsive, making it impossible to fetch new emails. The new 14.5.6 update should fix this problem for Outlook users who have installed OS X El Capitan and is a much better fix than Microsoft's previous workaround, which simply suggested users run OS X Yosemite.

  Microsoft Releases Office for Mac 2011 Update to Fix Outlook El Capitan Bug