We can't directly import new or offline OST file in Outlook. First, we need to convert OST file into PST file and then import the PST file in MS Outlook.
So to convert the OST file into PST format, use SysBud OST to PST Converter application. This software can convert multiple OST files into PST file format without changes in the original folder structure, meta properties, and Html formatting. It completely retrieves all inaccessible, orphaned, and damaged OSTR files and export them into PST file format. The application is able to export the unlimited size of the OST file into Microsoft PST format with all email, contact, calendar, notes, tasks, etc. The software supports all version of MS Outlook as well as easily installs in all Windows Systems.