I have had my account for 5 years and I recently went into my account settings on my Mac to just check my settings to allow me to setup my sons email account correctly and then post me entering my account settings I am getting this "Unable to Verify Account or Password" error popping up.  

I have changed my password to try and resolve the situation. - no luck

I do not have MFA set as I noticed 2 Factor Authentication can be an issue with Mac Mail- still can not access my mail on either my iPhone and or Mac Book - any suggestions.

I can not get my sons account setup either as its giving the same error