I saw a popup error in Mail on my MacBook Pro today, “Unable to verify account name or password.”
A bit of Googling found the answer.
Process to recover your macOS Mail and Inter net Accounts from the ‘Unable to ver i fy account name or pass word’ issue.
1: Open your email account in sys tem preferences.
2: Choose the email account to verify.
Note that your pass word field is blank.
3: Fill in the password.
4: Press Tab to move to the next field (Impor tant!).
5: Press OK again to force verification.
Then select the email account in the Mail app’s sidebar, right-click & select Synchronise account.”
All fixed. Not exactly an intuitive process.