It's the server which does not accept the password. I presume you also have an issue when sending new Write message, but password is ok for incoming. It would be helpful if you could post an image of the error message. Maybe you have the wrong smtp being used by the email address you are using to send. '''Check the smtp:''' * In 'Account Settings' * in left pane, scroll to bottom and click on 'Outgoing Server (SMTP)' and it should show you all the various smtp being used. * select each in turn and look for the one which has 'Username' = email address of account which has a problem sending. * Select it and then click on 'Edit' * Description: Enter email address = Username * Check all the server names, port etc are correct. * Click on OK Then make sure that email address mail account is actually using that smtp. * In Account Settings * select name of account * look bottom right for 'Outgoing Server (SMTP)' * It should say the email address for that account - it shows what you typed in 'Description' If it does not say email address of the account: * Click on the drop down icon to see options and select the correct one. * DO NOT click on 'Edit SMTP_Server' because you could end up editing something used by another account. Exit Thunderbird and allow a little time for background processes to complete. Start Thunderbird. Allow account to download first before trying to send an email. If prompted for password: # enter correct password # select checkbox to remember password # click on OK