If you setup your MFA from a cell phone (maybe with the Outlook app) it did not create an app password for you.  You will need to create one to be used for your email app and/or Outlook on the desktop.

Outlook on the desktop will NOT work properly without an app password.

To create/manage MFA app password(s), use this link or use the instructions below.

  1. Login to Office365.
  2. Click on your initial/picture at the upper right corner.
  3. Click My Account.
  4. Click Manage security and Privacy.
  5. Click Additional Security Verification.
  6. Click Create and manage app passwords.
  7. Click Create.   Enter a name as prompted (the name isn't important).
  8. The system will then create and show you the app password.  Note that this WILL NOT BE SHOWN AGAIN, so copy it and put it in a safe place.  
  9. Use the new app password for the mail app on your phone and Outlook on the desktop.