If you want to convert offline OST files to PST format without any extra efforts then you can try most trust-worthy and easy to use ZOOK OST to PST Converter software. It is developed with highly advanced algorithm which makes it fully safe and effective tool. The software quickly convert single or multiple OST file to PST format including emails, contacts, notes, attachments, journal, etc. Users can recover deleted or inaccessible data of OST file and export them Outlook PST file. It help to repair highly corrupted or damaged OST file and smoothly convert them into PST format without damaging any type data. It is compatible with all versions of Microsoft Outlook and Windows Operating Systems.

For more info- https://www.zooksoftware.com/ost-to-pst/