Using a simple approach to convert offline OST into PST files, I recommend the MailsDaddy OST to PST Converter utility. It is a powerful software solution for converting OST files to PST and various other formats. Below are some of its key features:

Retrieve data from orphaned, corrupted, or inaccessible OST files.
Recover and export data from deleted items.
Export options include PST, MSG, EML, RTF, EMLX, CSV (for contacts), HTML, and more.
Apply filters during the conversion process to refine your export.
Divide large OST files into smaller parts for easier management.
Batch conversion enables users to convert multiple OST files simultaneously without any hassle.
This program ensures complete data integrity during the conversion process.