Thunderbird is a free email application with easy customizations and set up, loaded with awesome features. It is default email application on various Linux distributions like Ubuntu. So first thing you need to do is visit your Gmail account to enable POP in Gmail.
Step-1
For doing this, click Gmail settings icon and select ‘Settings’ option from the drop down. Now select “Forwarding and POP/IMAP” tab then under “POP Download” click “Enable POP for all mail (even mail that’s already been downloaded)” just below the “1. Status“. Under “2. When messages are accessed with POP”, select “keep Gmail’s Copy in the inbox.
Step-2
From your Ubuntu Dash Home search and start Thunderbird then add new email account from File -> New -> Mail account. It will ask you to enter your name, your email address and password, then click “Continue“.
Step-3
Clicking the ‘Continue‘ button your Gmail settings will automatically be downloaded to Thunderbird.
Step-4
Select “POP” instead of “IMAP” for the incoming server and click ‘Create Account‘. You’re almost done. Just click “Get mail” and the backup will begin. Quitting the Thunderbird will stop your backup and when you need updating the “backup”, just open Thunderbird and it will start.