Sometimes add-ins can conflict with Outlook. Starting Outlook in safe mode, which starts Outlook without add-ins loaded, can tell you if an add-in is the problem.
  1. In the upper-left corner of Outlook, choose File > Options > Add-ins.

  2. At the bottom of the View and manage Office Add-ins, make sure the Manage box shows COM Add-ins, and then choose Go.

  3. As a precaution, when the COM Add-ins listing of your current add-ins opens, do one of the following:

    • Manually record the title of every selected add-in listed under Available Add-ins.

      or

    • Take a screenshot of the property sheet and save the image to a location of your choice.

  4. After you've captured the titles of the selected add-ins, clear all selected check boxes, and then choose OK.

    Caution: Click a check box to clear it. Don't select an add-in and choose Remove. If you have administrator rights, you could actually delete the add-in. For this troubleshooting exercise, you want to disable, not delete, an add-in.

  5. Choose File > Exit.