Cách backup toàn bộ dữ liệu gmail

 Select What You Want To Download

1. You’ll need to log into your Gmail account
2. Head to the ‘Download your data‘ page. Here you’ll be able to select all the products to be included in your download.
3. All the products will be ‘Selected’ by default. If you want to start fresh, click ‘Select None‘.
4. Scroll down, find ‘Mail‘ and select it
5. Choose to ‘Include all of your mail‘ or ‘Select labels‘
6. IF you’re ‘Selecting labels‘ you can choose from things like Drafts, Inbox, Chat, Spam, Imported, and so much more.

Choose The File Type

1. Decide if you want to download your archive or save it in the cloud.
2. Select .zip or .tgz
3. Select between 1GB and 50GB for your archive size

ref to: 

https://mycomputerworks.com/how-to-download-emails-gmail/