When you use Thunderbird's automatic account creation (Account Hub), it makes an educated guess as to the correct settings for your email provider. It usually gets it right, but not always. You can manually enter the settings, but you need to be armed with them before you begin. I found this Spectrum page with supposedly correct settings, but you may need to contact them to confirm: https://www.spectrum.net/support/internet/mobile-email-setup To manually configure an account, you will need to have the following details which can be supplied by your email provider: - incoming mail server and port (for example, "pop.example.com" and port 110 or "imap.example.com" and port 143) - outgoing mail server and port (for example, "smtp.example.com" and port 25) - security setting for the connection with the server (for example, "STARTTLS" or "SSL/TLS" and whether or not to use secure authentication) First, turn off "Account Hub" - see (in Windows) <Tools | Settings | General | Account Hub>. Read the following article for tips on how to set an account up manually: https://support.mozilla.org/en-US/kb/manual-account-configuration