MFA works great most of the time however it is a pain when it comes to applications that need to access your account which cannot perform the MFA dance. I’ve been using Office 365 for a long time and like a good citizen have MFA enabled for my account (in fact I have MFA enabled for everything that I can). If you have Office365 MFA enabled and Outlook constantly prompts you for a password for your Office365 account, you may need to enable Modern Authentication in your Office365 tenant.
