Check out the SysInspire OST to PST Converter software if you need to recover an Outlook OST file. This app is quite depressing. This software converts Outlook OST files to PST and a variety of other formats, including EML, HTML, Yahoo, Gmail, Office 365, EMLX, ICS, MSG, MBOX, vCard, and Zimbra. The email filtering feature allows you to convert only a subset of OST files based on a date range. From SysInspire's official website, you may get a free demo version of this utility.