Even with the new Google Gears Offline Gmail function in Google Labs, I still wanted to have a non-google-related backup of my Gmail account. After researching the various options, I found that the easiest way to do so is to set up an old fashioned POP3 account in Mozilla Thunderbird, and let it sit and send/receive for a a few days. Thunderbird makes it sickeningly easy to set up Gmail, as it includes all of the POP3 Gmail set-up information. No need to worry about enabling SSL and TLS ports. Ready to get started?
1. Download Mozilla Thunderbird here.
2. Install Thunderbird using the default settings
3. Open Thunderbird, and close out of any Wizard that may open.
4. Go to Tools > Account Settings. Then click the “add account” button at the bottom right.

5. Select “Gmail” and hit next.

6. Type in your name, and the username of your GMail account, and hit Next. Hit Finish on the following screen.
7. You should not be back in the “Account Settings” Window. Click on “Server Settings” under your Gmail Account. Change “Check for new messages” from the default setting of 10 Minutes, to something shorter, like 3 minutes.

8. Hit OK, and you should be in the main inbox for Thunderbird. Now, hit “Get Mail” or use the shortcut CTRL-Shift-T to start your messages downloading from Gmail.
9. Messages download in batches of around 50 to 100 messages per time. For large inboxes, it may take several days to download all of your messages.
10. I noticed a lot of older duplicate messages in my inbox, so I downloaded the handy Remove Duplicate Messages Add-on for Thunderbird.
11. After installing the Remove Duplicate Messages Add-on from Step 10. Right click on your Gmail Inbox, and select “Remove Duplicate Messages.”

12. In the next window, all of your duplicate messages will pop up. All you need to press is the “Delete Selected” button, which will delete all of your duplicate messages, but leave the original ones intact.