Microsoft and Exchange servers are the most popular and highest-rated applications. MS Outlook stores your mailbox items such as emails, contacts, calendars, etc. in OST file format, also known as an offline storage table. But sometimes Outlook users face the "OST is in use and inaccessible" error. If you are one of them, follow this content from top to bottom to solve your problem with no extra hassle.
For More Info: OST to PST Converter