OST vs PST and To Know Difference Between What is PST and OST

Written By Deepmala
Chirag Arora
Approved By Chirag Arora  
Published On October 3rd, 2023
Reading Time 6 Minutes Reading

If you are using Microsoft Outlook, then you will be aware about the Data Files created by it, which are OST and PST File. If not then we are going to discuss in this article about Microsoft Outlook and the difference between OST vs. PST.

Therefore, the topics we are going to cover in this article are:

What is Microsoft Outlook

Outlook is an E-mail client software/application available as a part of the MS Office suite, which provides the user with option to send, receive mails along with various other features like tasks, journals, calendar, contacts, notes, etc.

In addition, Outlook being a web-mail provider allows you to configure with other web-mail providers like G-mail, Yahoo, etc. You are thus able to access your accounts together on a single application.

There are two ways to setup Outlook depending upon the user’s needs and requirements.

  • MS Outlook as a Standalone application
  • MS Outlook with Exchange Server environment

Stand Alone Application: You require an e-mail account to set-up Outlook, as it is a provider for web-mail. Thus, the account configured with Outlook becomes the default account. More than one account can be configured in Outlook, one being the primary account and others, secondary.

MS Outlook with Exchange Server: Besides collaborative communication, connecting your Outlook to an Exchange Server enables setting up your account in such a way that you can continue to work even when you are not connected to a server. Thus, you are able to access your messages, contacts, etc., and make changes to it, which will be updated automatically once connection with the server is regained.

Types of Outlook Data Files (OST vs PST):

  • For Stand Alone Application – PST File (Personal Storage Table)
  • For Exchange Server (Cached Mode) – OST File (Online Storage Table)

Difference Between Outlook OST and PST Files:

With Outlook 2013 edition, Microsoft has changed the way how IMAP accounts are handled. With IMAP access of a mail account for Outlook 2013, an OST file gets created instead of PST.

MS Outlook automatically creates a .pst file for accounts like POP3, IMAP, Web-based email accounts on your system in the hard disk drive where all the data gets saved.

Connecting your Outlook profile to an Exchange Server creates an .ost file, which allows the user to work with their account even when not connected to the server and save the data in a mailbox on the server.

Let us now Discuss in Detail About .ost vs .pst difference

Personal Storage Table (PST): In Microsoft Outlook, PST is an Open File Format, which is used to create the copies of the messages, contacts, calendars, etc., on your computer from the account configured on Outlook. This PST is not related to the mailbox of your account thus is not bounded by any size limits.

On creating an account in Outlook, a default PST file is created. Multiple PST files can be created for a single account. This can happen when –

If the default file is archived and a new file is created now as default and this file can now be stored on local computer according to the user’s choice. With one PST being your default where all the Outlook Data will get saved.

A PST file can also be secured with a password to prevent from unauthorized access.

How to Manage Your PST File:

  1. If your PST file gets damaged or corrupted in any case, MS Outlook provides with an in-built tool to repair your damaged PST file. This tool is present in your computer programs in the file directory. Thus, it can be used as and when required.
  2. There are options to import or export your PST file, moving it to another location.
  3. MS provides with encryption setting so that the data remains intact.
  4. You can merge your PST files together, Archive them, Split them into segments, etc.

Size & Formats: Earlier versions (until 2002) of Outlook supported a maximum storage capacity up to 2 GB only with ANSI encoding. Whereas 2003 and onwards Outlook version provide with 20 GB of storage with UNICODE encoding. Outlook 2010 version’s default storage capacity is 50 GB.

Offline Storage Table (OST) unlike PST files, depend upon account configuration and cannot be opened individually. OST makes an Offline copy of every Outlook data item that exists on the mail server. In addition, it allows the user to work on those data items like editing the data, saving mails in draft, deleting or adding items etc. when there is no server connection. However, once the connection is obtained, all the changes made on the data items appear on the server that is, it synchronizes itself automatically when online. Thus helping the user work even when offline.

Understanding How OST File Works – When you are working on Outlook with no server connection i.e., offline mode, an exact copy of the mailbox is created by MS Outlook and is stored locally on the user’s client system. Each account on Outlook gets a single OST file, which is labeled as default. In addition, when MS Outlook turns online, data is synced.

OST files are of immense use as they keep your data safe and secure. However, it is not safe to rename or delete it as it may lead to data loss due to single creation from server itself.

In case of accidental deletion or corruption of your mailbox, OST files provide with the appropriate backups. Outlook provides with inbuilt scanost.exe tool to repair your corrupted or damaged data.

Storage Location: The location of Outlook Data File depends upon the operating system the user is using. Both Outlook OST and PST files are stored at the same location.


  • PST is used to store file locally whereas OST is an Offline storage used when no server connection is present.
  • PST file may be used for an Exchange set-up though is not recommended but unlike OST files, which are compatible only for an Exchange Server, is compatible with other servers too.
  • OST file allows its users to read, delete, compose, edit messages when Offline whereas PST does not.
  • OST is suited for domains with limited internet connections but such is not the case for PST files.