I want to use Thunderbird to download my Gmail messages as an offline backup. I generally followed the directions at http://www.webupd8.org/2011/03/how-t...underbird.html, although some of the steps were slightly different due to the age of the post.

But everything seemed to work. I started Thunderbird on my laptop and logged on to the email account I'd created. Thunderbird proceeded to download about 500 messages. Every time I quit and restarted Thunderbird, it would download about 500 additional messages. They were still in my Gmail. So far so good.

When I got home, I set up Thunderbird on my desktop (so I'd have 2 backups). I assumed that it would start downloading messages from the very beginning since Thunderbird on my desktop had no idea what my laptop had been doing. However, it didn't work that way.

It seems that my desktop started downloading messages where my laptop had left off. Apparently, the Gmail server is keeping track of my Thunderbird activity. This is a problem because I seek a single backup of all the messages in one place.

After some study, I discovered that the messages are stored in ~/.thunderbird/hreipadj.default/Mail/pop.googlemail.com/Inbox. Inbox is an actual file (not a folder) with the messages!

Other files in the pop.googlemail.com folder are Inbox.msf, Trash, Trash.msf, msgFilterRules.dat, and popstate.dat.

Is there a way for me to reset Thunderbird and/or the Gmail server and start over? Now that I know how it behaves, I can just download on one computer until it finishes. Alternatively, is there an easy way (or even a hard way) to merge the two Thunderbird inbox files, so that I will have a backup with all my Gmail messages together?