Steps to Back up Gmail Emails in PST Format
Step 1: Go to Gmail Account Setting and Enable IMAP option as shown on below screen.
Step 2: Now, you need to turn on Less secure apps. You can done this by opening this URL: https://www.google.com/settings/security/lesssecureapps
Step 3: In this step, you need to enter Gmail credentials.
Step 4: Check all folders/ custom folders and click on "Next" button to proceed the next step.
Step 5: In last, choose export option to create backup in desired format.