Once MFA has been activated for your EUI email address, you may need to re-configure the concerned email profile whitin Apple Mail by re-creating.

If the above still does not work, make sure to update Apple Mail and/or your macOS X operating system to the most up-to-date version.

IMPORTANT: your macOS X must be AT LEAST version 10.14 (Mojave) in order to support MFA!

If you cannot or do not wish to upgrade to macOS X 10.14 (Mojave), you will be unable to use Apple Mail with MFA. Please consider installing Microsoft Office 2016 and using Outlook, or you can use Outlook Web Access (EUI Webmail).