What is .ost File Extension?

Full Form of OST File

OST stands for Offline Storage Table/File. The acronym of OST defines the meaning & complete organization of data items like Emails, Calendars, Contacts etc while having connection with Exchange Server.

Overview of .ost file Extension

Offline Storage Table (OST) is a data file of offline Outlook while having connection with Microsoft Exchange Server. All email messages, calendars, contacts and other items are saved on the server. To have a copy of the data items on your local system, you can configure Outlook and use data files named as Offline Storage Table (OST). With the help of this you can access Cache Exchange Mode and access emails offline when a connection with Exchange Server is not available. It gets again synchronized with Exchange Server, whenever connection is re-established.

What is OST File Format?

OST is data file having replicas of Exchange Server mailbox on the personal computer that can be accessed in offline mode also. It is automatically saved with .ost extension whenever a profile is configured with Exchange Server. This OST file make it possible to access folders from server location when there is no network. A user can add, modify and delete content of the offline folder in the same way as in connected with server. Whenever a user performs the operation on data offline, it gets updated automatically when connected with server again. This is called a synchronization process of Outlook OST file with Exchange Server.

How To Access OST File?

MAPI profile, which created it originally is used to access an OST file. First, it checks the authentication of OST file with its original profile. If it does not match, it will refuse to open. It's all because OST file has encrypted cookie from the unique ID of each mailbox. When connection to server is made, then only a user can access this unique ID. Each time Outlook is started for accessing an OST file, the system registry and the encryption key is checked first. If both matches then only access to OST is provided. Mail data of OST file is stored in B-tree form and organized hierarchically in nodes (512 bytes) and leaf form.

The main reason of why OST file cannot be opened is when users use different profile to access the database other than the one that originally created it. If a user has changed the location on server or deleted the mailbox, in that case also users lose access to OST file.

OST File Location in Windows

Offline Data File (.ost) has different location at different versions of Microsoft Windows. OST file locations are specified below:

Windows Vista & Windows 7: Supports Microsoft Outlook 2007 has location:
drive:\Users\user_name\AppData\Local\Microsoft\Outlook\

Windows XP: Supports Microsoft Outlook 2010 has location:
drive:\Documents and Settings\user_name\My Documents\Outlook files\

Windows XP: Supports Microsoft Outlook 2000/2003/2007 has location:
drive:\Documents and Settings\user_name\Local Settings\Application Data\Microsoft\Outlook\

Importance of using OST Files

There are various advantages of OST files are available that makes a user to work continuously with data safety irrespective of any server crash.

1. The OST file has a major importance when working offline. A user can use this procedure to work in secure and safe environment. It never allows user to lose access to data irrespective of connection with Exchange Server.
2. Offline data files (.ost) provides great flexibility of working offline without connecting with a server.
3. OST files serves as backup of accidental deleted emails or of corrupted data in mailbox. A user can easily recover all emails as well as export OST into PST whenever they want.

Limitations of Offline OST Data File

Everything has an advantages and disadvantages associated with it. Therefore, OST file also has some disadvantages. It is helpful for the email profile to which it belongs to. If a user email profile gets deleted or damaged, then in that case OST file can't be accessed and it becomes very hard for MS Outlook to extract data. Sometimes a user is leaving its company and want to access the data afterwards also. In that case it is not possible for a user to open OST file in some other email profile. However, OST files are accessible by the account that created it.

Conclusion

The above discussed section all about what is .ost file extension and the data storage location of OST file, specifications, advantages, and the limitations. As introduced that the OST file is data storage file used by MS Outlook named as Offline Storage File. It allows users to access data in online as well as offline mode. It is basically created at the time of creating a connection with Exchange Server. A user can access, modify & delete data in offline mode too and the changes will get synchronized with Exchange Server as the connection re-establishes. It is only accessible by the profile using which the Offilne storage file have created. OST File has different storage location on personal computer according to the Windows OS versions. As it gives an advantage of using OST file in offline, it has also some disadvantages or limitations.