I'm trying to open OST file in C#. I'm using below code but still facing error. I got stuck while creating an application. filter = "[ReceivedTime] >= '" + dtpStartDate.Value.ToString("dd/MM/yyyy 12:00 AM") + "' and [ReceivedTime] <= '" + dtpEndDate.Value.ToString("dd/MM/yyyy 11:59 PM") + "'"; Outlook.Application outlookApp = GetApplicationObject(); Outlook.Folder root = outlookApp.Session.DefaultStore.GetRootFolder() as Outlook.Folder; EnumerateFolders(root); Outlook.MAPIFolder inboxFolder = outlookApp.Session.GetDefaultFolder(Outlook.OlDefaultFolders.olFolderInbox); inboxTable = CreateTable(); After the search on Web, I have found few sources where the solution of this problem is provided. But I don't know which solution will fix my problem. Please refer below sources. https://community.rackspace.com/general/f/general-discussion-forum/8881/how-to-open-ost-file-using-c-code https://www.nopcommerce.com/boards/t/56083/how-to-open-ost-file-using-c-net.aspx https://www.stellarinfo.com/convert-ost-to-pst.php http://forums.codeguru.com/showthread.php?562219-How-Do-I-Open-OST-file-using-C Please help.