There may be multiple steps. Did you already close that email account ''at the provider'' so that anyone sending to that account will get a message that the account does not exist? You may want to make sure that is done first so you don't miss any valuable messages. Then in Thunderbird, do you want to keep the old mail associated with that account? Depending on how the account is configured in Thunderbird, deleting the account may also delete your local copy of the mail, so... don't be a rush to delete the account until you know the consequences. Instead, in the short term, you can modify the Send/Receive settings so Thunderbird does not automatically check for messages on that account. There is a section of this support article on automatic scheduling: [[Sending and Receiving Messages on Thunderbird]].