You can check this by clicking settings>privacy&security and viewing the passwords set there.

Did you edit the stored password?

• In Settings > Privacy & Security
• Scroll down to Passwords section
• click on 'Saved Passwords'
• Click on 'Show Passwords'

If prompted for password: If you have previously set up to use 'Primary Password' then enter the Primary Password - do not be confused this is not a mail account password. If you have not set up 'Primary Password' then you ay see a 'Windows Security' window asking for password. When you start computer and enter user account password to see desktop - that is the password you need to enter.

Mail account will have two lines, one for incoming and one for outgoing smtp. It sounds like your incoming is ok - so check the smtp line - does it have same username and password as the incoming?

• Right click on smtp:// line for account and select 'Edit Password'
• Completely clear all content and then carefully type the correct password.
• When finished, click on 'Close'

Now Exit Thunderbird , wait a few moments for background processes to complete and restart Thunderbird. It should then use the updated password.

Well, I have got it working now. Last night when I got the error message I also had a prompt to reset the password, which I did, and it still didn't send mail. Today I tried again and entered the new password and it worked. I had assumed, when it says use same password for both incoming and outgoing servers, that when I changed the password, Thunderbird would change it for both, but clearly I was wrong. Though why, when at the initial setup, you enter a password and it sets the same one for both servers automatically. Something which could be improved I think.