new account

I just opened my Thunderbird e-mail account, did thunderbid only access emails from my sbcglobal account email account or did TB download the the 100,000+ SBCglobal emails to a thunderbird file that I can continure to access?. I believe that AT&T is going to delete my sbcglobal email account as I have canceled my AT&T internet service. I see sbcglobal messages in thunderbird that go back to 2008 that I would like to read again. Will these messages disapper when AT&T disables the SBCglobal email account.