OST Vs PST, Differences Between OST and PST Files

Megha Chouhan
Megha Chouhan | Updated On - 20 Jul 2022 |

Read time: 5 minutes

OST and PST files are very familiar terms for all Microsoft Outlook users. Both are known as the data storage files of Outlook.

MS Outlook is a part of the MS Office Suite and works as an e-mail client application with some mind-blowing features like a calendar, task manager, contact manager, journal, and a lot more.
Offline Storage Table (OST) saves data for offline use.
And Personal Storage Table (PST) stores data on the client’s local disk.

Both used to store mailbox items, such as emails, attachments, contacts, notes, etc. OST files can be converted to PST file format and vice versa when needed.

If you are facing any issue with your local OST file location, you can simply change the location of the OST file in Outlook.

For more deep understanding, today in this blog we will cover different points on OST vs. PST.

Introduction to MS Outlook

MS Outlook was introduced in 1997 by Microsoft for personal information management. Now, it is a part of the MS Office Suite as an email client. It serves the purpose of both, a stand-alone application, and a server-client. This application is designed to use by an individual as an email client-server and by an Organization which requires shared features like a mailbox, calendar, appointments, etc. There are two types of Outlook Data Files used by Outlook i.e. OST and PST.

Introduction to OST

OST (Offline Storage Files) allow access to mailbox data in offline mode on the local machine upon registration with Exchange Server using Microsoft Outlook. Through the first use when MS outlook gets connected with the server, it gets automatically created. Once the file is created, the data is synchronized with the email server so that it is available offline as well in the case of offline mode. Even you can create emails and other data items in the OST file even in the absence of a connection to the server, but these will not be synchronized with the server. And when the connection is established, the local file is synchronized with the server again so that both the server and the local copy are at the same level of information. Even using the Import/Export feature of MS Outlook, one can export contacts from OST to PST. An OST file is saved with a .ost extension.

Introduction to PST

PST (Personal Folders file) is an Outlook data file that stores your messages and other items on your computer. This is the most common file in which information in Outlook is used by small organizations and single users. They may be having one or more email accounts. The most common types of accounts are referred to by their Internet protocol named POP3. In POP3 configuration, data is stored as a PST file with a .pst extension.


Learn the below points to understand the basic difference between OST and PST files.

  • OST files can be used even in the absence of connection with the Exchange Server in offline mode, and when the connection is established, it synchronizes itself with the Exchange Server mailboxes. OST keeps copies of items i.e., mailbox items saved on the email server.
  • PST doesn’t allow to do this as this file is used for POP3, IMAP, and webmail accounts. These .pst files are created when users want to backup emails locally.
  • The OST files mainly support Microsoft Exchange Server.
  • PST files are compatible with other services.
  • OST is encrypted with MAPEntryID GUID key and needs authentication from the linked MAPI profile. Hence can’t be accessed or imported into any other Outlook profile.
  • PST file is importable and can be easily accessed through any Outlook profile.
  • OST synchronizes automatically and appears on the server without any downloading.
  • PST requires downloading emails and files locally and becomes a separate file.
  • OST files are harder to get damaged but once in a while due to malware or virus intrusion, system crash, synchronization errors, profile corruption, etc. it gets damaged, and then it turns into inaccessible mode and becomes orphaned.
  • PST files can easily get corrupt due to sudden system shutdown, PC crash, power outage, etc. Even though it stores multi-gigabyte data, they become unstable or even inaccessible when grows too large. One can easily access password-protected PST files by using tools available on the internet.

Difference between OST and PST files based on common criteria

Criteria OST PST
Dependency This can’t be moved from the Exchange server independently. Possible to move and separately make a database Outlook file.
Server Support It supports mainly an Exchange server It supports Exchange Server and other mail servers also
Security Encrypted using MAPIEntryID GUID key Not encrypted and is easy to access through a third-party tool
Error or Damage Hard to get damaged Easily get corrupt or damaged
Import Only access by using the original MAPI profile Easy to import into any Outlook account
Online/Offline It supports offline access to the mailbox It does not support offline access to mailbox items
Portability Server dependent and can’t be ported It is portable and can be saved anywhere on any local system
Synchronization Data automatically get synced using an internet connection Not possible to sync automatically
Benefits Users keep working with domains irrespective of server availability It works great when users want to have a backup

How to access inaccessible OST files?

To access OST files, you can convert OST files into PST. Then you can easily access the mailbox items. Using the third-party OST to PST converter can easily help you out. By having this tool, you can save OST emails to Gmail, Outlook.com, and other IMAP servers.

PST files are very easy to access. To save the data from theft or corruption, you can use this PST converter tool which converts the PST files into DBX, MBOX, MSG, EML, TXT, RTF, HTML, and MHTML. It easily converts large to small and even corrupt OST files to the desired formats. Using this tool, it is easy to convert deleted mail items also.


Whether it’s OST vs PST, MS Outlook is used to keep all information using both these file formats. OST has its own importance as it allows offline access to the mailbox data; one can easily send new messages even when the system is offline or disconnected from the Exchange Server. OST files are highly encrypted whereas PST files are easy to access without having a password by using a third-party tool. Still, one can access the OST file and convert OST to PST format or export it to live Exchange or Office 365 by using a Kernel for OST to PST Converter.