You'll need to clarify some things. Thunderbird is not an "account", it's an email agent, that is, a program that interfaces with your email servers and allows you to send and receive email. What happens when you try to retrieve email? Do you get any error messages? What about when you try to send? You can try to verify your email settings, which should be available from your email provider (maybe on their Help web site.) You're looking for: IMAP or POP3 server name IMAP or POP3 port number user name (usually your email address) connection security setting (SSL, TLS, STARTTLS) authentication method (normal password, OAuth2, etc.s) SMTP Server Name: smtp.comcast.net SMTP Port: 465 Authentication method Connection Security Check that information against what you already find in the Accounts Settings.