I would say the ConverterTools OST to PST Converter tool is the perfect option for you. This tool is recommended by many experts and users. It can smoothly import your OST data to Gmail and other email clients, for example, Hotmail, Office 365, Thunderbird, Hotmail, and so on, with their attachments like email messages, calendars, contacts, notes, tasks, etc. It has the capability to transfer OST mailboxes to multiple file formats, like PST, PDF, EML, MSG, MBOX, and so on, in bulk. Moreover, it includes the functionality to skip all copies of OST files during the OST importing process and allows for the maintenance of folder hierarchy based on their original files.