Authentication not working with Office 365 and multi-factor authentication

Dears,

I-am an IT admin for office 365 and when i enabled MFA for the user he cannot recieve or sent emails an it gave that the password i
Or username is incorrect
Please advise ASAP

BEST regards

Usually cases like this are covered by the documentation of large email providers.

And/Or have been solved by other users on the internet.

I did it at the begining and my accout worked until yesterday, yesterday it stopped. I dont know why? but it worked on the different app