Open Microsoft OST File - Version 3.5 You need to recover some old emails in your .ost file. When you try to open the outlook .ost file in Outlook and then got the message "outlook .ost file cannot be accessed because it has been configured for use with a different mailbox" and face the necessity to convert all information from Microsoft Exchange (files with the .ost extension) into files of the Microsoft Outlook email client (.pst files) - OST2PST procedure. SysTools Open Microsoft OST File software effectively solves problem OST to PST Conversion. You can use the Open Microsoft Outlook OST File tool to easily move your messages, contacts, notes, meetings, reminders, tasks and all other information. Open Microsoft OST File tool work on offline file like .ost file. This Open OST File tool use to open OST file in Outlook PST file with complete item of OST file with time and date. Microsoft OST to PST tool has some wonderful feature to support all the version of Outlook 2010, 2007, 2003, 2000 & 98 etc. And it store on the Windows operating system and make good capability to do reliable work and it simply pick data from Exchange