BT yahoo have more than one server which seems to get out of synch on occasions, so first check both of these work ok.

Are you able to logon to BT Mail to see webmail ? https://home.bt.com/ If no : then you need to use the forgotten password link to gain access and set up password. If you cannot access this webmail then Thunderbird will not be able either.

If yes: Please check you can also logon to the yahoo logon - see link below: https://login.yahoo.com

Not the https://home.bt.com/ one which you probably usually use. If you keep getting redirected then clear the cache and retry as you need to get this one: https://login.yahoo.com Then logon using exactly the same information as you used to logon to webmail at BT Mail.

Then make sure Thunderbird is using exactly the same password:

• 'Menu icon' > 'Options' > 'Options' > Security' > 'Passwords' tab
• click on 'Saved Passwords' button
• click on 'Show Passwords' button
• Check password is correct.
• TO alter password. right click on relevant mail account lines and select 'Edit Password'

• click on 'Close'
• click on 'OK'

Exit Thunderbird and restart.

Thank you so much - BT insisted it wasn't their problem!

Not fixed after all! Tried quitting and restarting but no joy.