re :I have changed my password with Cox in order to send Emails, Have you updated this in thunderbird? 'Menu icon' > 'Options' > 'Options' > Security' > Passwords' tab click on 'Saved Passwords' button click on 'Show Passwords' button locate the smtp://mailbox for the account. If there is more than one 'smtp://' for the that cox account, remove the incorrect one. Is the password correct? Regardless..right click on that smtp account line and select 'Edit Password' completely clear the contents and type in the correct password. click on 'Close' click on OK Close and restart Thunderbird. Test sending. Please report back on results.