Thunderbird connects to providers servers if you have the correct server settings. Email providers configure their servers. If your provider is not smart enough to give you the correct settings, find another one.

What do you have for the incoming and outgoing server settings? They should be mail.twc.com for both the incoming (IMAP port 143 or POP port 110) and outgoing (port 587) servers, with Connection security = None, authentication = password, transmitted insecurely and User name = email address.

If you still have problems, it may be helpful to reset the password. Also, disable any security program from scanning email if it's in place.

I did find this page with Spectrum settings. http://www.spectrum.net/support/internet/email-settings/

Thanks sfhowes. I starting having this problem about a month ago. I could still receive my e-mails with Thunderbird but could no longer send using Thunderbird. I called Spectrum and they knew about the problem and said they were working on it. The next time I called they said they had a work around since they changed the outgoing server to mail.twc.com unfortunately they told me to change my setting for connection security. After reading your answer I noticed your setting for connection security to None was what I had for the receiving server. I went back and changed it to none for the outgoing mail server and all is now well.