Hello,(OST file) is offline storage table. Which is creates when your MS Outlook (Email client) comes in an environment of Exchange server. We called this file as offline table file because it facilitate you to do offline work without any network connectivity and after synchronization it automatically established connection with Exchange server. It consists of no. of folders such as-emails, contacts, Tasks, Notes, Calendars, Journal, Reminders and Meeting etc. And offline folders used for managing large email database on a client’s systems.
Sometimes OST file becomes corrupt due to several reasons like virus attacks, bad sectors, email headers and accidental shut down etc, And to restore OST file data it is important to convert OST in PST that requires application which is
OST to PST Converter Software. Users are confuse in the selection of software because now a days there are so many solution are available in online or market, but i suggest you to try this Tool.
For download this application click on :

Recover email data along with attachments and email properties, calendar entries, notes, appointments, journals, drafts as well as permanently deleted email items. It can save recovered emails in different formats i.e. PST, MSG, DBX, and EML formats. This software provides you best facility to split your large PST file into small PST file 1GB up to 5GB. It works on OST file versions-5.0, 5.5, 2000, 2003, 2007, 2010, 2013, 2016.
To know more about this information visit :
http://www.softmagnat.com/ost-to-pst-converter.html