If you need to convert offline OST to Outlook PST, then use eSoftTools OST to PST Converter. You can convert multiple OST files to PST format without creating any error. The software can provide the highest level of security. During the conversion process, it can preserve all emails properties and data like contacts, calendars, emails, attachments, etc. This application works with all versions of Windows OS and MS Outlook 2003, 2007, 2010, 2013, 2016, and 2019.