The most effective and top rated solution to convert OST to PST without Outlook, which I have found is EmailsGuru
OST to PST Converter. It allow users to convert OST file to PST format. This tool preserves all email data, including attachments and folder structures during the conversion process. It is capable to fix corrupted or damaged OST file and convert them into PST format. Moreover, it can convert OST file to PST without installing Outlook in your computer. Users can also use a free trial version and convert or migrate 25 items from an OST file to PST file.
