You can also try the professional BLR **OST to PST Converter Tool **to convert Outlook OST file to PST file format with complete details and attachments. It is one of the best tools to bulk move Outlook offline OST file to PST with all emails, contacts, calendars, and other items without Outlook. It has a very simple GUI, anyone can easily handle and manage the tool without having any problem. It was compatible with Windows OS including Windows 11. You can also use the free demo version of the program without any cost.