If you want to convert OST to PST without Outlook, use the eSoftTools OST to PST converter software. It can convert OST to PST and various formats like Office 365,EML, PST, Gmail,Yahoo Mail, Office 365, Zimbra, MBOX, MSG, ICS, vCard, EMLX, and other formats. This tool does not require any Outlook application while conversion of OST file. After conversion, you can easily open or access OST file in Outlook without any errors.