Maybe if you post a screenshot of your SMTP server settings, someone here may have suggestions.

Thanks David - I'll do my best but I recall being able to view SMTP, POP3 and IMAP settings but they appear to be scant and I do not appear to be able to access them. Also the password listing facility in Thunderbird is beginning to look somewhat empty. Pretty certain that I've not personally deleted them!

Sorry. Will carry out another check up. I am also having difficulties with Virgin Media emails generally as I read a rumor they were attempting to get rid of @ntlworld.com. Is there any truth in that.

to see SMTP settings - click 'acount settings' - scroll down left side to 'Outgoing servers (SMTP) and do screenshot of the account's SMTP settings there. I know nothing about ntlworld.com Passwords are at settings>privacy&security: click 'saved passwords' and then 'show passwords'