Difference Between OST and PST

If you are a Microsoft 365, MS Exchange Account, POP3 or IMAP account user, then you’ll definitely know about the PST and OST files.

Both PST and OST are known as the data storing files for such servers. You can easily convert an OST file to a PST one and vice versa according to the requirement.


The main difference between OST and PST is that OST files store data for offline utilization while the PST format saves data in the users local drive. An OST file is saved with a .ost extension, while a PST file is saved with a .pst extension.


OST files create the possibility for Outlook to work offline and automatically sync to Outlook when having access to an internet connection. It can also be used in an MS exchange server in an exchange environment.

This enables the clients or users to compose, delete, read, as well as reply to emails in offline mode.

Whereas PST mode cannot be used in an MS exchange server but is used on other servers. In fact, HTTP and IMAP use only PST folder files.

Your mails, journals, contacts, calendars, and various other mailbox components that are saved locally are also stored in the PST format.  

Comparison Table Between OST and PST

Parameters of ComparisonOSTPST
Server compatibilityCompatible with all Exchange server versions.Compatible with other servers other than MS Exchange server.
PortabilityServer dependent and can’t be port.It is portable and can be located anyplace on any local system.
Dependency factorCan’t be transferred from the Exchange server individually.Possible to separately make a database Outlook file.
Sync possibilityData gets automatically synced when provided with a net connection.No auto-syncing can be done.
BenefitsUsed when users want to work with domains where the net connection is low/poor.  Utilized when user want to have a backup of Outlook components.

What is OST?

OST is basically your offline file mode in MS outlook. Offline Storage Files drafts mailbox data of the user, for offline mode on the local system. It does so by registering with Exchange Server taking Microsoft Outlook in use.

It is automatically made during the very first usage of Microsoft Outlook with server connectivity. Once the folder is composed, the data get arranged with the server of mail for offline availability.

Clients can make mails and other data components in OST format even in the offline mode but, the data won’t be synchronized when offline.

Once your server is connected to an internet connection, the local copy and the server will be at the same pitch to sync information. 

The contents that OST format can sync are:

  1. Headers: Descriptive identifiers that will give the sender name, message subject line, message receiving time and the message size.
  2. Full items:  Includes the header, message body with any sort of attachments like pictures or objects. You can delete, add or change the items of the offline file.

You can also port items between folders, view content of your public offline folder, and send messages that are there in your offline Outbox.

Also, new messages are saved in the server inbox, and other users can delete, add or change contents in the folder.

What is PST?

In the computing language, PST or Personal Storage Table is an exclusive file format created by Microsoft to save copies of calendar events, messages and other components in their software program like Windows messaging and Microsoft Outlook.

The merit of PST is that they are easily portable and can be moved from one Outlook user to another. While owning the portability advantage, it also has a few security issues.

PST files are not designed to work as multi-gigabyte email archives. Due to this, subsequent data loss and corruption can be recurring occurrence.

PST files also own emails that can’t be archived nicely. They are thus, not always put into an appropriate retention classification system or deletion.

With that, PST files can be password protected but, a simple search on the net can discover many programs that could easily crack the passwords you’ve kept. This basically puts the client data at risk.

PST files are frequently used mail storing format, underlying all email solutions of Microsoft. In any Microsoft-based surrounding, getting how to manage and secure PST files is vital for blocking legal issues, attacks or data loss utilizing archived mail data.

Main Differences Between OST and PST

  1. OST is called Offline Storage Folder, while PST is called Personal or Online Storage Folder.
  2. OST files let the user read, reply, compose and view the mails even in the offline approach, whereas in the PST file format, you can’t enjoy the advantage of such a feature.
  3. OST files just support the Microsoft exchange server. As for the PST file format, you can use the exchange mode (though not recommended).
  4. OST files could be worked upon in online as well as offline mode, while PST could be used for the files and data that are saved locally. 
  5. OST depends solely on the account configuration and can’t be opened individually. As for PST, there is no such feature found. 


MS Outlook stores all of its information in either OST or PST file format. This basically depends on the factor that the client has arranged all of their Outlook properties in what manner. For this, the info may or may not be encrypted or compressed.

With the Outlook edition of 2013, Microsoft changed how IMAP accounts should be handled. With the IMAP approach for Outlook 2013 for a mail account, an OST file automatically gets created instead of a PST one.

It does so for IMAP, POP3, and web-based mail accounts on the system you are working on in the hard drive, where basically all your data is stored and saved.

When you link your account with an Exchange server, an OST file is created, which lets the client work on their accounts while they’re offline and save their data in the server mailbox.


  1. https://www.convertost.org/exchange-installation-and-recovery.pdf

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