Sorry, I am quite new to these problems, to be honest a lot frustrating. I do not know if this email address concerned has this two step authentication, also no idea or how I would find out if I have less secure apps to access. Where would I also find an app specific password, other than mine of course.
If the account is Yahoo then it’s likely this is the problem:
https://help.yahoo.com/kb/add-two-step-verification-extra-security-sln5013.html
https://help.yahoo.com/kb/generate-third-party-passwords-sln15241.html
There doesn’t seem to be any allow less secure apps to access the account so the above solutions are required.