Microsoft Outlook is a key component in most workspaces, and the Outlook data like email, calendar, contacts, etc are either stored on an OST(Offline Storage Table) or PST (Personal Storage Table) depending on whether the account is POP, IMAP, Exchange, or Office 365.
Though they serve the same purpose, OST and PST files exhibit different characteristics in terms of how they interact with the email server. The upcoming sections in this article will discuss them in detail without technical jargon.
What is OST?
A .ost (Offline Storage Table) file stores Outlook data offline. Changes made to the OST file are synchronized with the server when the device is connected to the network.
OST files are created when you set up an Exchange account in Outlook. The OST file is saved on the user’s computer and is used to store a local copy of the user’s mailbox data.
Typically, OST files are stored in a hidden folder on your computer. You can find the exact location in Outlook settings.
By default, the maximum size of an OST file is 50GB on Outlook 2010 and you can change the limit by modifying the registry settings.
Advantages of OST:
- Real-time synchronization: OST files provide a local copy of the mailbox that can be constantly updated with the server.
- Large mailbox support: OST files can handle large mailboxes.
- Reduced email server load: As OST files store a local copy the server is not engaged with requests for every action.
Disadvantages of OST:
- Potential data loss if not synchronized: If OST files are not regularly synchronized with the server, there’s a risk of losing data.
- Limited accessibility: OST files are linked to a specific Outlook profile and cannot be readily accessed by other applications or users.
What is PST?
A .pst (Personal Storage Table) file also stores the outlook data on your computer, primarily used on POP3 accounts. You can also configure IMAP accounts to use PST files.
Typically the PST files are used for archiving or transferring data between Outlook versions or different computers.
PST files are classified into two types: ANSI and UNICODE. Outlook 2000 and 2002 used the ANSI format with a maximum limit of up to 2GB. Outlook 2003 later uses the UNICODE format, which has a maximum file size ranging from 20GB to 50 GB which can be changed by modifying the registry settings.
Advantages of PST:
- Independent of email server: PST files can be standalone, which makes it easy to port.
- Archiving and Backup: PST files are commonly used for archiving and backup purposes.
Disadvantages of PST:
- Manual synchronization: Unlike OST, PST files require manual synchronization with the email server. This can be time-consuming.
- Chances of corruption: PST files are more susceptible to corruption compared to OST files due to their structure
OST vs PST: Key Differences
| Attribute | OST | PST |
| Synchronization | Changes made to the offline file are synchronized with the server automatically when an internet connection is established. | Changes made to a PST file are local and must be manually synchronized with the email server. |
| Usage | Primarily used in Microsoft Exchange Server environments. | The POP3 and IMAP account types use PST files. |
| Server options | .ost files work with Exchange servers | .pst files work with exchange servers and other servers too |
| Data access | Allows users to read, edit, compose, or delete mails in offline mode | Doesn’t allow to perform any actions in the offline mode. |
| Portability | OST files are dependent on the server, and can’t be ported. | It is portable and can be moved anywhere on the device. |
| Security | OST files offer a higher level of built-in security | PST files are not encrypted by default. |
OST and PST File Locations
Here is the default location of the Outlook PST and OST data files:
OST File Default Locations in Outlook 2016, 2019, and Microsoft 365:
C:\Users\\AppData\Local\Microsoft\Outlook\
PST File Default Locations in Outlook 2016, 2019, and Microsoft 365:
C:\Users\\Documents\Outlook Files\
Common OST and PST Issues
OST
Synchronization Errors: Emails, calendar entries, or other data fail to sync when there is a connection issue between Outlook and the Exchange server or IMAP account.
Access Denied Errors: Outlook fails to open, with error messages, or is unable to access due to a permission issue or improper shutdown that made OST inaccessible.
Oversized OST: Outlook may become slow due to the file exceeding the recommended size limits.
PST
Corruption: PST files can be corrupted due to improper shutdowns, virus attacks, or exceeding the PST file size limit. You may see “Outlook.pst cannot be found” or refuse to open the PST file when you try accessing it.
Import/Export Errors: Errors while importing or exporting data to a PST file to a Mac or other platforms can end up in partial or failed data transfer, leading to missing or duplicated data.
Unable to copy or move PST file: A corrupt PST file or large PST file can prevent moving emails to the PST file
Managing OST and PST Files
- Regular Backups: Create regular backups of your PST files. OST files are typically synchronized with the server, but having a local backup is still recommended.
- File Size Management: Keep an eye on the size of your OST and PST files. Large files can impact performance.
- Archiving: Archive old emails to reduce file size and improve performance.
- Regular Compaction: Compact your PST files to optimize space. For OST files, this is usually handled automatically.
- Defragmentation: Defragment your PST file to improve access time, but this is less necessary with modern operating systems.
Conclusion
We hope this article helped you understand all there is about Outlook data files. I.e., OST and PST files You can opt for either of those as per your needs.
If you ever run into a corrupt Outlook PST file or OST file, you can use dedicated Outlook repair tools to fix the issue.
