OST Vs PST, Differences Between OST and PST Files

Megha Chouhan
Megha Chouhan linkedin | Updated On - December 13, 2022 |

Read time 7 minutes

Summary: Are you an Outlook user who is confused about OST and PST files and don’t know how it differs from each other? Then, you are not alone. Many users want to differentiate between these two files. So, you must refer to this blog as it will give you detailed information about both these data files. Also, if you are unable to access OST files, this will help you resolve the specific problem.

If you are among millions of people who use Outlook applications for email communication, you may have come across of OST and PST files. These data storage files save the mailbox items such as email messages, calendars, contacts, and notes. Both these files are stored in your personal system and are helpful in recovering mailbox items when any corruption occurs.

MS Outlook is a part of the MS Office Suite and works as an e-mail client application with mind-blowing features like a calendar, task manager, contact manager, journal, and a lot more. This application offers several innovative features that make it unique from other options. But many Outlook users are still confused about the data files included in it, i.e., OST and PST. They don’t know exactly what it is actually and what the difference is between OST and PST. Now, you need not worry; this blog will guide you to get detailed information about both data files.

Introduction to OST

OST (Offline Storage Files) allow access to mailbox data offline on the local machine upon registration with Exchange Server using Microsoft Outlook. This file gets automatically created after establishing connection with the server and is saved in a system with .ost extension. If you are facing any issue with your local OST file location, you can simply change the location of the OST file in Outlook.


Instant Solution

Suggested software to access OST file’s data in Outlook. Try Kernel for OST to PST Converter to covert OST file to PST format.

Introduction to PST

PST (Personal Folders file) is an Outlook data file that stores your messages and other items on your computer. It is the most common file in which small organizations and single users use information in Outlook. They may have 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. In addition, these files are also secured from unauthorized access with a password.

Now it’s time to know the differences between the OST and PST files data files in Outlook.


If you are still confused between these two data files, you need not worry, as here we listed the top differences between OST and PST files.

  • OST files allow users to work offline even in the absence of a connection with the exchange server. After the connection restores, it synchronizes itself with the Exchange Server mailboxes. This file keeps copies of items that are saved on the email server.
  • PST doesn’t allow 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 requiring any downloading.
  • PST synchronization requires downloading emails and local files.
  • OST files are harder to get damaged, but it can occasionally happen due to various reasons such as malware or virus intrusion, system crashes, synchronization errors, profile corruption, etc. It turns into inaccessible mode and becomes orphaned.
  • PST files can easily corrupt due to sudden system shutdown, PC crashes, power outages, etc. Even though it stores multi-gigabyte data, they become unstable or even inaccessible when grows too large. Also, note that password-protected PST files can easily be accessed 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 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 after restoring the 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 tools is a reliable option to do so as it can save OST emails to Gmail, Outlook.com, and other IMAP servers efficiently.

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 various file formats such as DBX, MBOX, MSG, EML, TXT, RTF, HTML, and MHTML. It easily converts corrupt OST files to the desired formats. In addition, you can also recover your deleted emails with this tool.


Whether it’s OST vs PST, MS Outlook keeps all information using both these file formats. OST has its own importance as it allows offline access to 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 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.

Q- Should I use PST or OST?

A- To choose any one among both these data files, you must be clear about your preferences. If you want to back up Outlook items on your system, you must use PST files. But, if you have an Exchange account and want to work offline without network connectivity, you must prefer OST files.

Q- Why do I need to convert OST to PST?

A- The OST files store the entire mailbox items of MS Outlook. It is synchronized with the exchange server, and if you want to access your mailbox items in the case of exchange server downtime or maintenance, it is required to export OST to PST and then import it to Outlook. This conversion becomes important if your organization is shifting and you want to migrate data to a different system.

Q- Can you have multiple OST files in MS Outlook?

A- It might be possible when multiple Outlook IMAP profiles are configured with the account. Note that this file generates every time you log in to your Outlook account. There can be other reasons responsible for generating the OST file, such as a corrupted profile or Active Directory account, access to a shared account, etc.

Q- What is the maximum size of the OST file?

A- The overall size of the OST and PST files for the latest Outlook version is 50 GB. If you bring changes to the Windows registry, you can increase or decrease the file size limit. Also, note that the large-sized OST and PST files result in abrupt Outlook behavior and performance issues.

Q- What happens if I delete the OST file?

A- There will be no data loss if you delete the OST file from your system, as it can download from the exchange server again. If you plan to do so for any reason, your exchange profile must be in good condition. Also, many professionals recommend keeping a backup of files.

Kernel for OST to PST