I'm not having that problem, but here are my settings. How do they compare with yours? IMAP: Server name: imap.comcast.net Port: 993 user name: my Comcast email address connection security: SSL/TLS authentication method: Normal password SMTP: Server Name: smtp.comcast.net Port: 465 User Name: my Comcast email address Connection Security: SSL/TLS Authentication method: Normal password =================== You could try deleting your passwords for those servers from the password manager (Settings | Privacy & Security | Saved Passwords,) after which you should be prompted to input it again. I recently discovered that there were some leftover entries there that referenced old credentials - they weren't causing a problem for me, but maybe they are for you? I deleted them anyway. I recently had a problem with another email account, not Comcast, where my mail stopped working in Thunderbird. I eventually deleted the account and re-added it, letting Thunderbird choose the settings from its database. That revealed that the provider had changed their settings without letting me know. It works now. I would not want to do that with Comcast because I have years and years worth of mail that it would take forever to download again, but if all else failed, I might resort to that.