Using webmail, I can log onto the mailboxes and view messages as normal, albeit very slow (which is why I generally don't use webmail, preferring the Mail app within Mac software.) I have just tried to send myself an email and it says as before with the 'SMTP' error message. I have tried a few times, with the same result.
I am a legacy email account after leaving Plusnet broadband a while ago. I have not changed the password recently.
Thanks.