We would need to see any and all error messages you see, complete and verbatim to make more accurate suggestions. But the first thing you should do is confirm your email server settings, which may have changed during the migration. Here's Greenby's instructions page about that: https://greenby.com/support/knowledgebase/article/29 For lack of information, I'm going to make some guesses... If this is an IMAP account, the token (which is related to your password, but is not your password) may no longer be valid. You can start the authentication process fresh by deleting all current password/tokens for that account , which can be found at <Settings | Privacy & Security | Passwords | Saved Passwords>. Also, remove all cookies for that account. They can be found at: <Settings | Privacy & Security | Web Content | Show Cookies>. Restart Thunderbird and you should be prompted for your credentials, so have you user ID and password handy.