Thanks for all the replies. Sorry about my initial grumpiness, but I can't afford to lose all my messages on Gmail.

Quote Originally Posted by gifford View Post
If you allow Thundrbird to download gmail as an IMAP account, you would have mail physically on your computer.
The email is physically on my computer now with the POP account. All the messages are in a huge file called ~/.thunderbird/hreipadj.default/Mail/pop.googlemail.com/Inbox. I know they're there because I opened it in a text editor and looked.

Quote Originally Posted by cross37 View Post
I also use thunderbird and POP3 to backup my email. Gmail remembers which emails have been downloaded via pop3 so that they will not be downloaded again. Here is how to reset this and start over, making all the email downloadable again.

[instructions omitted]
This trick worked for me and more or less fixes my original problem. However, it would be nice if I could have complete but independent backups on my laptop and desktop. I will experiment with IMAP, which is what almost everyone recommends. So I won't mark the thread solved yet.

Can I create separate IMAP and POP accounts in Thunderbird for the same Gmail account?

Thanks for all the help. As far as I know I haven't lost any messages yet.