Close what account ? It would really be helpful if you explained what you are talking about. All email addresses are dependent upon whomever created them for you. Some may be offered by ISP others maybe free eg: gmail If you want to cancel an account so that the email address no longer exists then you cancel via the company which offers the email address. If you created a mail account in Thunderbird for a particular email address to download emails from server then you can easily remove it. * Menu icon > Account Settings * Select name of account in Left Pane * Click on 'Account Actions * Select :'Remove Account'. * Restart Thunderbird.