With 2FA enabled, attempts to use the regular password associated with the email account will result in a continued prompt for a correct password or failure to connect or send.
Users with Two-Factor Authentication (2FA) enabled on their Office 365 account, or other services require the use of App Passwords for use in Outlook and RDB ProNet. App Passwords are codes that give an app or device permission to access your Office 365 account.
To create an App Password for use in Outlook or RDB ProNet:
Log into Office 365.
Click the users name in the top right and click My account.
Click Security and Privacy settings.
Click Additional Security Verification or Two Factor Verification settings.
Click App Passwords to generate individual passwords for Outlook and RDB ProNet.
Note: For further instructions read this Microsoft article.
Use the password in place of the user’s regular password in Microsoft Outlook and in RDB ProNet an App Password will need to be entered into:
Click Options then click User Preferences.
Click Mail Service.
Type in the app password.
Click Save and close.