OST vs PST, What’s the difference?

Know about Outlook OST and PST files

Microsoft Outlook is a personal information manager and email application developed by Microsoft. It is part of the Microsoft Office suite of applications and is widely used by businesses and individuals to manage their email, calendar, contacts, tasks, and other personal information.

Outlook is designed to integrate with Microsoft Exchange Server, enabling users to send and receive email, share calendars and schedule appointments, and collaborate on projects with other Exchange users. In addition to its email and personal information management features, Outlook also includes a number of other tools, such as a task manager, a journal, and a note-taking feature.

OST and PST files are the fundamental to the proper functioning of Microsoft Outlook. However, what is the difference between them? This is the question that bugs many a people especially rookies. But before we proceed to answer the question we must first understand what constitutes OST and PST files as we know it and what purposes they serve.

What is an Outlook PST file?

A PST (Personal Storage Table) file is a type of data file used by the Microsoft Outlook email client when you set up a POP account in Outlook. It stores email messages, contacts, tasks, calendar items, and other data locally on your computer and does not sync with your email server. Unlike an OST file, which is used to store a copy of data from your email account, a PST file is not connected to a specific email account on the server and is used to store data locally on the computer.

The PST file enables you to backup and transfer the email data between computers or to archive it for future reference. Additionally, the data stored in a PST file is not tied to a specific email account and can be used to store data from multiple email accounts in a single location, making it easy to access and manage all of your email and personal information in one place.

Features and uses of Outlook PST files

1. Data Storage: PST files enable you to store and manage email messages, contacts, tasks, calendar items, and other data locally on your computer.
   
2. Data Backup: PST files provide an easy way for you to backup your emails, ensuring that the data is protected in the event of a computer crash or other data loss.
   
3. Data Archiving: PST files can be used to archive old or infrequently used email data, helping you to reduce the size of your mailbox and improve its performance.
   
4. Data Transfer: PST files can be transferred between computers, making it easy to access email and personal information on multiple devices. They are portable and can be opened and imported into Outlook to retrieve emails and messages. 
   
5. Multiple Email Accounts: PST files can be used to store data from multiple email accounts in a single location, enabling you to access and manage all of the email data from one place.
6. Improved Email Performance: By reducing the size of your email account and improving the management of email data, PST files can help improve the performance Outlook.

What is an OST file?

An OST (Offline Storage Table) file is a type of data file used by the Microsoft Outlook email client. It serves as a local copy of email messages, contacts, tasks, calendar items, and other data stored in your email account. When Outlook is used in offline mode, the data from the email account is stored in an OST file on your computer, enabling you to continue accessing and working with your email data even if you do not have an internet connection. For instance, if Outlook will not connect to the server, you can still access your mail items from the OST. The OST file is synchronized with the email account once an internet connection is reestablished, ensuring that the local and server-based data remains up-to-date. In short, an OST file enables you to access the email data while offline and ensures that any changes you make are automatically synced with the Exchange server.

Features and uses of Outlook OST files

1. Offline Mailbox Access: OST files enable you to access your email and other mailbox data stored, even when you do not have an internet connection.
   
2. Data Synchronization: When an internet connection is reestablished, OST files are synchronized with the email account, ensuring that the local and server-based data remains up-to-date. For instance, when you have Outlook synchronization errors, you cannot access your email data. In such cases you must convert the OST file to PST format to access your emails.
   
3. Improved Email Performance: By storing a copy of data from your email account locally on your computer, OST files can help to improve the performance of Outlook and reduce the need to fetch data from the server every time. 
   
4. Data Backup: OST files provide an additional level of backup for your email and personal information, helping to ensure that the data is protected even if the email account is lost or corrupted.
5. Tied to an Exchange profile: Unlike a PST file, an OST file is associated with your Exchange profile with a MAPIEntryID GUID key that uniquely identifies the email account. If the Exchange server goes offline or if the OST file is corrupted due to Outlook crash, you must rebuild the OST file or perform conversion to PST format  to retrieve all your email data.

Where are the OST and PST files stored in the computer?

The location of the OST and PST files can vary depending on the version of Outlook you use, but the OST file is typically stored inside the AppData folder and the PST file is stored in the Outlook Files folder in Windows.

OST File Location

To locate the OST file in Windows computers, navigate to the following path:

C:\Users<Username>\AppData\Local\Microsoft\Outlook\

Here are the steps to find the location of OST files directly from the Outlook client:

Step 1: Open Outlook and go to the File menu 

• Start by opening the Microsoft Outlook client.
• In the Outlook client, click on the ‘File’ tab in the ribbon.

Step 2: Click Account Settings to open Email accounts

• In the ‘File’ tab, select ‘Account Settings’ 
• Select the ‘Account Settings’ option from the list

Step 3: Select Data files to check the Outlook data file location

• Go to the ‘Data Files’ tab in the Account Settings page
• Click ‘Open File Location’ to open the folder where the OST file for the mailbox account is stored. 
• You can see the full file path in the address bar at the top of the window

PST file location 

In Windows, the PST files are typically stored in the following location:

C:\Users<Username>\Documents\Outlook Files\

Outlook OST vs PST files, difference explained

The main difference between the two Outlook data files is that OST (Offline Storage Table) files are used to store a cached copy of your email, contacts, and calendar information when you use Microsoft Outlook with an Exchange account. PST (Personal Storage Table) files, on the other hand, are used to store a local copy of your mailbox data when you have configured an IMAP or POP email account.

The OST file is synchronized with the Exchange server, enabling you to access your email, contacts, and calendar information even when you’re offline. The PST file is used when you want to create an additional backup of your mailbox data or archive them for storage. PST files can also be used to import and export data between different Outlook profiles or to different email clients.

Another difference between OST and PST files lies in their functionality, the way they are tied to specific email accounts, and their method of synchronization and backup. 
OST files are tied to a specific Exchange account and cannot be used with other email accounts, while PST files can be used with any email account and can be easily imported and exported to other email clients. OST files are automatically synchronized with the Exchange server, while PST files do not offer automatic synchronization and must be manually backed up. Additionally, OST files are typically larger in size than PST files, as they contain a cached copy of all of your email, contacts, and calendar information.

While both OST and PST files cannot be opened directly, PST files can be transferred from one computer to another and imported into Outlook whereas the OST files cannot be accessed independent of the Outlook profile that creates them. This is the primary reason why PST files are preferred for archiving mailboxes as they are easily manageable and portable. While OST files sync data automatically with the server, the PST files don’t offer any such provision.

Here’s a table summarizing the differences between OST and PST files in Microsoft Outlook:

Feature	OST (Offline Storage Table)	PST (Personal Storage Table)
Purpose	Stores a cached copy of email, contacts, and calendar information when using Outlook with an Exchange account	Stores a local copy of email, contacts, and calendar information, or as a backup for email, contacts, and calendar information
Functionality	To store an offline copy of the mailbox data	Mainly for archiving, backup and email storage
Email account configuration	Exchange account	POP3, IMAP and other mail servers
Email Account Compatibility	Tied to a specific Exchange account and cannot be used with other email accounts	Can be used with any email account and can be easily imported and exported to other email clients
Synchronization	Automatically synchronized with the Exchange server	No automatic synchronization and must be manually backed up
Encryption	OST file is encrypted with a MAPIEntryID GUID key that authenticates with the Exchange profile	PST files are not internally encrypted and can be opened in MS Outlook
Accessibility	Can only be accessed through the associated Exchange account and Microsoft Outlook client	Can be accessed through any email client that supports the PST file format
Portability	Not portable	Portable
Import Functionality	OST files cannot be imported into Outlook	PST files can be imported into Outlook
File Size	Typically larger, as they contain a cached copy of all email, contacts, and calendar information	Typically smaller, only contains locally stored information
File Management	OST files are managed automatically by the Exchange server and Microsoft Outlook	PST files must be managed manually by the user
File Size Limit	Limited by the Exchange server mailbox storage space	Limited by the available hard drive space on the local computer
Search Functionality	Search functionality is limited compared to PST files	PST files offer advanced search functionality through the Microsoft Outlook client
Sharing	OST files cannot be shared between multiple computers or users	PST files can be easily shared between multiple computers or users
Synchronization Speed	Faster synchronization speeds compared to PST files	Slower synchronization speeds compared to OST files

How to open and view an Outlook OST file without Outlook?

From the preceding section, it is clear that OST files cannot be moved or transferred to another computer because of their association with the Exchange profile. To view the OST file without Outlook, you can use EdbMails OST to PST converter software to open and convert all your mailbox data from the OST file to PST. After the export operation is completed, you can import the PST file into Outlook to retrieve all your emails.  

Tip: EdbMails provides a user-friendly interface and is easy to use, even for those with limited technical expertise. The software also offers advanced features such as selective item conversion, the ability to preview converted items, and an OST to Office 365 converter tool to import OST files to Office 365 and Exchange.

What are the reasons for OST/PST file corruption?

Although the OST and PST files are important for the proper functioning of Outlook, there are several reasons why Outlook data files cannot be opened and become inaccessible including:

1. Abrupt Termination of Outlook: If Microsoft Outlook is closed unexpectedly or crashes while an OST or PST file is being used, it can cause the file to become corrupt.
2. Oversized PST File: PST files have a size limit, and when they overgrow in size, they can become corrupt.
3. Network Connectivity Issues: If an OST file becomes disconnected from the Exchange server due to network connectivity issues or Outlook fails to sync properly with the Exchange server, it can cause corruption to the file.
4. Virus or Malware Attack: Virus or malware attacks can cause damage to the OST or PST file, making the data inaccessible.
5. Hard Drive Failure: If the hard drive containing the OST or PST file fails, it can result in corruption to the file.
6. Power Outage or System Crash: A sudden power outage or system crash can cause corruption to the OST or PST file.
7. Improper Upgrade of Outlook: If an upgrade to Microsoft Outlook is not performed properly, it can cause corruption to the OST or PST file.
8. Incorrect File Operations: Incorrect operations on the OST or PST file, such as deleting, moving, or renaming the file, can cause corruption.

Tip: It’s important to regularly back up your OST and PST files to prevent data loss in case of file corruption. Learn how to backup Outlook emails to an external hard drive.

How to convert OST files to PST?

In case you have an orphaned OST file and need to extract the data or if you are faced with a corrupt or inaccessible OST file due to sync related issues, you can make use of EdbMails OST converter application to repair and convert the OST to PST. It also comes with a free OST viewer that allows you to open OST files without requiring Outlook.

1. Download and install EdbMails on your computer.
2. Select the OST file from your computer for conversion
3. Select the mail items and ‘Export OST to PST’. That’s it!

After the conversion is complete, you will have a PST file that can be opened and viewed using any email client that supports the PST file format.

To summarize

1. OST files enable offline viewing of Exchange mailboxes.
2. OST files are only accessible through the Outlook profile that created them.
3. PST files are copies of Exchange mailboxes that are used for backup and archiving purposes. 
4. PST files are portable and can be imported directly into Outlook.

Frequently Asked Questions (FAQ)

1. Should I use OST or PST?
   The choice between an OST file and a PST file depends on your specific email setup and needs. If you have an Exchange account and want the convenience of being able to access your email, contacts, and calendar information even when you’re offline, an OST file may be the best option. However, if you have an IMAP or POP account, or if you want more control over your data for backup and archiving, a PST file may be a better choice.
2. What is the need to convert OST to PST?
   Here is a list of reasons why you might need to switch and convert the OST file to PST.
   
   
   1. Data Backup and Recovery: Converting OST to PST can provide a backup of important email, contacts, and calendar data in case the original OST file becomes corrupt or is lost.
   2. Data Migration: When transitioning from one email platform to another, it may be necessary to convert the OST file to a PST file in order to transfer the data to the new platform.
   3. Access to Offline Data: OST files are designed to be used in offline mode with Microsoft Exchange Server. If an individual is no longer using Exchange Server or needs to access their data on a different device, they can convert the OST file to a PST file to access the data. Another reason to perform the conversion is when your mailbox has been temporarily moved on Microsoft Exchange server and you want to restore your email data.
   4. Improved File Management: Converting an OST file to a PST file can provide better file management by freeing up space on the Exchange server and enabling you to replicate the PST files across a network.
   5. Improved Data Security: Converting OST to PST can provide an additional layer of security for important email, contacts, and calendar data. The PST file can be stored on a local device or on a remote server, providing a backup in case of system failure or other data loss events.
3. Why is Outlook creating OST instead of PST?
   Outlook creates OST files instead of PST files because of the way it is designed to interact with Microsoft Exchange Server. OST files are created when the Cached Exchange mode is enabled in Outlook. This data file is used to store a cached copy of the data from an Exchange account, enabling you to access the mailbox data offline. In contrast, PST files are used to store email, contacts, and calendar data in a standalone format, without the need for a connection to an Exchange Server. PST files are typically used for data backup, data migration, or to store data from IMAP, POP and non-Exchange email accounts.
4. Will I lose emails if I delete the OST file?
   Deleting an OST file will not necessarily result in the loss of emails. OST files are used to store a cached copy of the data from a Microsoft Exchange account, and the original data on the Exchange Server is not affected by the deletion of the OST file.However, if the OST file was the only copy of the email data, and it was not backed up or converted to a PST file before being deleted, then the email data will be lost. Additionally, if the OST file became corrupt before it was deleted, the email data may also be lost. As a result, it is important to ensure that a backup or conversion of the OST file is performed to avoid data loss.
5. Can I copy the OST file to a new computer?
   Yes, you can copy an OST file to a new computer. However, it is important to note that an OST file is tied to a specific Microsoft Exchange Server account, so simply copying the OST file to a new computer will not allow you to access the email, contacts, and calendar data stored in the file.
   When you set up a Microsoft Exchange account in Outlook on the new computer with the same email address as the original one, Outlook creates a new OST file and synchronizes it with the data on the Exchange Server. To open the Outlook OST file on another computer and access your mailbox data from your old computer, you must convert the OST to PST.