Select Allow for Trust Gmail to access via Google Gears :
Back up Gmail data using Offline mode Picture 6
Select the types of shortcuts to create and click OK :
Back up Gmail data using Offline mode Picture 7
And wait a few minutes, Google will complete the installation process and download the necessary email data to the computer. This period of course depends on the number of email users:
Back up Gmail data using Offline mode Picture 8
Having done all of the above, we have completed backing up Gmail data to the computer using Offline mode. To open the mechanism to control this mode, click on the small green check icon above the right corner of Gmail, below the account name:
Back up Gmail data using Offline mode Picture 9
On the other hand, if you want to know the Google Gears data storage location, enter the following path in the Run box:
% UserProfile% AppDataLocalGoogleChromeUser DataDefaultPlugin DataGoogle Gears
and copy the mail.google.com folder:
Back up Gmail data using Offline mode Picture 10
Good luck!