I would like to mention here ost to pst converter free from KDETools software that effortlessly transfer OST to Outlook PST, Zimbra, Gmail, EML, EMLX, vCard, ICS, MSG, Office 365, Live Exchange server, MBOX and etc. Along with its quickly works to transfer original Emails properties such as- TO, Bcc, Cc, subject, date, and etc. to import OST to PST Outlook format easily.
I recommend OST to PST Converter tool (DataRepairTools). User can use this converter for converting OST files, as well as save recovered items in several formats like EML, MSG, PST, PDF and HTML. The trial version is limited to recover 20 email items from each folder. If you want to recover all emails so quickly purchase the full version. It profoundly scans OST orphan issue and preserves your mailbox into a new PST file with 100% accuracy. The tool supports all versions of MS Outlook and Windows OS.
There are multiple third party tools available on the internet, you just need to find the right solution. I have used Softaken OST to PST Converter tool. when I required the same issue and got the accurate result. The software works on all Windows versions. A free demo version of this tool is also available few emails can easily be converted into each format.