You enter the same password you use to access webmail - you do not invent a 'new' password that has not been set up in webmail account. You also need to select the checkbox to 'Remember Password' before you click on 'OK' OR you access where saved passwords are stored and edit the stored password so it is correct. Settings > Privacy & Security Click on 'Saved Passwords' click on 'Show Passwords' You will see two lines for that account. mailbox://account.... and smtp://account.... Right click on each line in turn and select 'Edit Password' Completely clear the contents and carefull retype the correct password. click on 'Close' Exit Thunderbird - wait a few moments for background processes to complete and restart Thunderbird.