Open Gmail in a web browser
Sign in to your Google account
Click the Google apps menu
Open Google Takeout
Deselect all products
Select Mail
Choose the export format
Choose the delivery method
Set the file size and export frequency
Click Create export
Wait for the backup to be prepared
Download the backup file from the provided link
Save the file to your computer or external storage
Verify the downloaded backup file
Keep the backup in a secure location