Backup GMail to Thunderbird ( IMAP )

1. Download and install Thunderbird.
2. Run Thunderbird.
3. Provide email address and password during automatic configuration.
4. Allow access to GMail when prompted by Google.
5. Allow Thunderbird to do initial synchronization. Default setting of Thunderbird is to download for all folders.
6. Go offline and proceed with the prompt to download messages for offline use. Download progress should be displayed at the bottom of the Thunderbird window.
7. Go to General Settings > Offline Settings. Turn off “Automatically follow detected online state” and under “Manual state when starting up”, select “Offline".
   
   
   
8. Review messages in offline state to check if all messages have been downloaded.

Optionally, if the backup is for archiving an offline copy that will be stored in an external storage, you can download Portable Thunderbird, and use the same steps above for backing up your email.