An Introduction to Outlook Data File Types

Outlook stores data (emails, contacts, calendars and other items) in two default formats OST and PST. Outlook stores data in OST (Offline Storage Table) file format when it is connected to Exchange mail server using cache exchange format for offline accessing of mails in client computer. If the client system is configured using POP (Post office Protocol), a standard email receiving protocol, then Outlook data files are stored in PST (Personal Storage Table) file format. Sometimes these Outlook data files are inaccessible to user because of sudden damage or corruption of the files. The reasons for the corruption are numerous including sudden drive, network or device failure.

PST Files- An Introduction

Outlook allows user to create a local database called personal database which contains folders and archive mails. A PST file represents a message repository which contains a hierarchy of folders. These subfolders can contain messages, which may themselves contain attachments. You can find Information about folders, mails and attachments by seeing properties of PST folders. 

Characteristics of PST files

• Personal folders contain email messages and other Outlook content.
• PSTs are always stored on client system.
• PSTs are portable. You can copy, move PST from one system to other and access it.
• PST can act as backup for individual users.
• Heavy size PST is more susceptible to corruption so it is advised to split PST if it is oversized.

Drawback of PST Files

1. Security & Management Issues: Once the data is in PST file of user system, the server admin has no control over it. If you as a server admin want to find all copies of a certain email you simply can’t with this scenario.   
2. More Space Required: The data in PST files took more space as compared to on Server. 
3. Complex in Nature: PST file can get corrupted or become misplaced (sometimes lost entirely) because PST files are not designed for access over the network instead it is meant to be stored in local hard drive which complicates the backup and management process.

Difference between Personal Archive and PST

Personal archives allow administrators to provide larger storage solutions for users, while still providing access to all email. It provides a second location for storing older, rarely accessed emails. A personal archive can only be accessed by Outlook 2010 or newer or with Outlook Web App. A personal archive and a primary mailbox for a user do not have to be stored in the same mailbox database.

OST File- An Introduction

OST files are created when you (client) connected to mail Server (Exchange Server) using cache exchange mode. Cached Exchange Mode creates a local copy (which resides in client computer) of the data stored on the Exchange Server. Client can access this cache copy for most operations, speeding response times. Outlook and the Exchange Server synchronize the local (cache copy) and server data (original stored data) time to time.

Characteristics of OST files

• Allow users to work with their mails and other Outlook data items even when they are not connected to exchange server. 
• Unlike PST files which can be backed up individually, OST files are tied to the mail account configuration and cannot be opened or backed up individually. 
• The data stored in OST files get synchronized itself with your exchange server mailbox when you get online with Exchange Server. 
• Like PST file OST can be corrupted also. 
• You can make changes to the contents of an offline folder exactly as you can for a folder on a server.