“account error” on mail

Mail as stopped working, it has a error message, “account error”. I have deleted the account and redone it, I have tried various ideas I found on the web, if I go into iCloud.com all my emails are there.

The mail connection doctor, gives me this

SMTP - connection to server; login not required.

IMAP - Trying to log in to this IMAP account failed. Verify that the username and password are correct.

this as not changed since I started, all I have now is no email at all!