The best way is usually used to Open OST File Without Exchange Server by using the eSoftTools OST to PST Converter software. The tool can assist the client to recover all OST file data such as emails, notes, journals, attachments, etc, that convert OST files into OST or many other files like EML, EMLX, HTML, MSG, vCard, PST, and others. Using this application user migrate their all the data of OST mailbox like emails, sent-items, deleted-items, drafts, outbox contacts, inbox, calendars, notes (To, Bcc, Cc, Subject, From, Object, Date and Time) Into newly created Outlook PST file.
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OST file used when user contact exchange server for email some times there are so many resign to corrupted exchange server and ost file is not used for user to view email dux data recovery ost to pst converter software on the best software to convert ost file data in to a pst file dux data recovery support all the version of the ost file. for more info https://www.duxdatarecovery.com/ost-to-pst-recovery.php