There are several reasons which force users to import Outlook PST files to Gmail mailboxes, and you can have your reason. Whatever the reason, if you have a single PST file to import, I suggest creating an Outlook profile of Gmail and using the Import/export utility to import PST. However, if you've multiple PST files, then the only reliable way is to use an automated tool, and the Shoviv Gmail backup tool (https://www.shoviv.com/gmail-backup-tool.html) is at the top of professionals' listicles.
Shoviv Gmail Backup tool
As the name indicates, it is a backup tool for Gmail users and also allows importing PST files to Gmail. Hence, you will get a multi-purpose utility at a single cost. While importing PST to Gmail, the software offers several user-oriented features. Let me describe its process so you'll get an idea about software features and working.
How to import Outlook PST file to Gmail using Shoviv?
• Install and open the tool in your system.
• Click on the Export button and Add PST files and server name.
• Map PST files with Gmail mailboxes.
• Use filter options on the date and folder filter basis.
• Setup thread counts and mailbox login attempts and check the Run job immediately checkbox.
• Voila, the software will start to import PST files to Gmail mailboxes.