Difference Between OST and PST Files

When it comes to managing emails in Microsoft Outlook, two important file types come into play OST and PST. Both are used to store mailbox data such as emails, contacts, and calendars, but they serve very different purposes. In this article, we’ll explain what OST and PST files are, how they work, and the key differences between them.
Fig 1: Difference Between OST and PST Files

🔹 What is an OST File?

OST (Offline Storage Table) files are used when you’re working with Exchange, IMAP, or Office 365 accounts.

They store a synchronized copy of your mailbox data offline, allowing you to access emails and other items even when you’re not connected to the internet. Once you reconnect, Outlook automatically synchronizes any changes with the server.

Key Features of OST Files:

Works with Exchange, IMAP, and Office 365 accounts
Stores mailbox data offline
Can be used without internet connection (syncs when back online)
Linked to a specific email profile and device
Helps improve productivity and accessibility in environments with limited connectivity

Example:

If you’re traveling or working in an area with poor internet access, you can still compose emails in Outlook. Once you reconnect, Outlook automatically sends them from your OST file to the mail server.

🔹 What is a PST File?

PST (Personal Storage Table) files are used for POP3 accounts, email backups, and archiving.

Unlike OST, PST files store your mailbox data locally on your computer and are not connected to any mail server. This means you can easily move PST files between systems or use them to restore or archive old emails.

Key Features of PST Files:

Used with POP3 accounts, or for backup/archive purposes
Stores emails, contacts, and calendars locally
Can be moved or transferred from one computer to another
Not dependent on Microsoft Exchange Server
Ideal for data backups and long-term email storage

Example:

If you’re switching computers or want to save old emails for future reference, you can export your mailbox as a PST file and import it later.

🔸 Key Differences Between OST and PST Files

Feature	OST File	PST File
Usage	Works with Exchange, IMAP &	Used for POP3, Archive & Backup
Data Storage	Synchronized with mail server	Stored locally on your computer
Offline Access	Available (syncs when online)	Available anytime
Portability	Linked to a specific profile & system	Can be moved across systems
Dependency	Dependent on Exchange/Server	Independent from Exchange Server
Best For	Working offline with server sync	Backup and archiving data

💡 In Simple Words

OST = Work Offline with Server Sync
PST = Backup / Archive Data File

If you want to access your Outlook data while offline and sync automatically when back online — use OST.

If you need to back up, archive, or move your mailbox data — use PST.

⚙️ Managing OST and PST Files in Outlook

To view or manage your data files in Microsoft Outlook:

Open Outlook
Go to File → Account Settings → Data Files
You’ll see all your OST and PST files listed here
From here, you can open, export, or back up your mailbox data

🧠 Final Thoughts

Understanding the difference between OST and PST files is essential for IT professionals, system administrators, and Outlook users.

While OST keeps your mailbox synchronized with the server for seamless offline use, PST provides a flexible way to back up or transfer your data securely.

Both play a critical role in ensuring smooth email management, data recovery, and migration within Microsoft Outlook.