Are you a previous MS Outlook Email client user and recently shifted to Mozilla
Thunderbird. All your stored email data are saved in PST file format in Outlook. To transfer email data from a PST file to Thunderbird, you need a professional software solution such as the Shoviv IMAP Gmail Email restore tool. This tool can import PST as well as MBOX, EML, and MSG email files into Gmail. All you need is to download and install the mentioned tool and import any size of PST into thunderbird.