All mail accounts need to use a password to access the server. This is the same password you use to access the webmail account using a browser. It sounds like you entered a password in the beginning and selected the option for Thunderbird to remember it. Usually, the same password is used for incoming and outgoing mail. Can you receie mail ok? If yes, then that password is clearly still ok and being used. This is where your password will be stored: Tools > Options > Security > Passwords tab clickon 'Saved Passwords' Click on 'Show Passwords' button Is there a password for the mailbox and SMTP mail account? Note the password. If you only have an issue with the SMTP - sending of emails. select the SMTP password click on 'Remove' Click on 'Close' Click on 'Ok. Close Thunderbird. Wait a few moments for background processes to complete. Restart Thunderbird. TRy to send email. At prompt enter the password. Select the option for Password Manager to remember the password. Click on Ok To test password: Try to use that password to logon to your webmail account using a browser. If you get access then you know that password is good.