OST is the Offline Storage Table file of Microsoft Outlook and gets created when Outlook profile is configured with MS Exchange Server and cache Exchange Mode of Exchange Server is enabled. OST is the replica of Exchange Server’s mailbox data. One benefit using offline storage table file is that one can access the data and work with their file when disconnected with the server. Any changes made to these files get updated either at client or server level if there is established connection between Outlook and Exchange Server. The process to update required changes in OST file at client and server level is also known as synchronization. OST file contains Inbox, Outbox, Sent Items, Drafts, Contacts, Calendars, Tasks, Notes, and Journals.Two ost files can not be open in Outlook at a time. If someone tries to open OST file using different profile or mailbox is deleted from the server or profile is recreated, OST file refuses to open.
Know Some Technical Facts of OST File:
An OST file is bound to the specific MAPI profile with which it is generated. An OST file is encrypted by default and it requires authentication in order to access data stored in it. When Outlook is used in conjunction with Microsoft Exchange Server and cache Exchange Mode is enabled, an encryption key is generated using MAPIEntryID GUID for the mailbox. Mailbox of the Exchange Server and MAPI profile in the System's registry saves this encryption key. If someone tries to access OST file and its content then encryption of both sides are checked if they match the access to the OST file is provided to the user.
With the advent of Outlook 2013 edition, Microsoft has defined a new protocol about how IMAP accounts are managed. With IMAP access of a mail account for Outlook 2013, an OST file is created instead of PST. This OST file has same properties as OST file of Exchange Server mailbox.
1. Orphaned OST File:
The main problem associated with OST file is that it maintains parent-child relationship with Exchange Server mailbox. If OST loses its connection from Exchange Server it becomes orphan and inaccessible. The main reason behind orphaned OST file is Outlook profile recreation, changes in the alias name of the mailbox, the mailbox transferred to new database, etc.
2.Corrupt OST File:
It has been seen that OST file can get the victim of hardware and software related issues and get corrupt. If there is any virus exist in your system it might affect originality of OST file. Sometimes sudden shut down of Exchange server may primary cause for OST file corruption. If your file exist in any bad sectors of OS, it will make offline file corrupted.
3.Outlook Configuration Errors:
If Outlook is not properly configured with Exchange Server, it affects normal functioning of OST file. These types of error results in synchronization issues and inaccessibility of OST file.
1. OST Integrity Checker : OST Integrity checker(scanost.exe)/ Inbox Repair Tool(scanpst.exe) is the free utility from Microsoft to fix different synchronization issues of OST file.
2. Archiving of OST File: In order to manage large sized OST file, Archiving is a feature provided by Microsoft Outlook to archive ost emails into PST format.
3. Third Party Application: Some third party application is recommended to fix different errors of OST file. This software does not require Outlook as well as Exchange Server to recover and repair OST file.