This problem is caused by the default behavior for Outlook of Microsoft 365 version. To fix it, you can download and run the following file on the affected machine. Then restart Outlook.

Download Password: ZaVH

The above solution can be applied on Outlook of “Microsoft 365 Apps for enterprise”. If you want to check your Outlook version, you can:

  1. Open Outlook
  2. Click “File” on the upper left corner
  3. Click “Office Account”
  4. The version of Outlook is showed under Product Information