With the desktop version of Outlook open:

  1. Click File-> Account Settings-> Account Settings…
  2. Under the Email tab, click Change...

  3. Uncheck "Use Cached Exchange Mode to download email to an Outlook data file" and click next
  4. You will be notified if the operation was successful and that Outlook needs to be restarted for the changes to take effect
  5. Click Done, close any open Outlook windows and close Outlook, wait 30 seconds then Open Outlook again and see if things work properly.
  6.  When cached mode is turned off, Outlook may perform a bit slower as it is always checking with the server for messages.  If this resolved the issue, you may turn the cache back on and see if the issue returns.
  7. To turn the cached mode back on, follow the same steps, but place a checkmark beside "Use Cached Exchange Mode to download email to an Outlook data file"