My business partner's husband has a Comcast account with 30,000+ e-mails going back to 2008. He wants to save these e-mails to his computer before he deletes them from the online server. I installed Thunderbird on his computer and configured the settings for a POP account. When I checked the email, Thunderbird downloaded 5000+ e-mails dating back to August 2014. I tried checking the e-mail again and it only downloaded the new messages that had come in. How do I get it to download all 30,000 e-mails?