What Is the Difference Between a PST File & an OST File?

By Benny Taylor

PST and OST files are Outlook email storage files
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The OST and PST files are both used by Microsoft Outlook email software to store messages and other data. However, the two file types contain other important differences.


Microsoft Outlook is a well-known software package used for email and personal information management. You can use Outlook as a standalone email client on an individual computer, or as a way to interface with a corporate email system running Microsoft Exchange server. The PST and OST files store Outlook data on a Windows computer.


PST files are typically used to store Outlook data on a computer using Outlook as a standard email client, which is downloading mail from an online source such as a POP3 mailbox. PST files are a necessity when Outlook is used this way. OST files store messages and other data in the same way but are offline storage files used alongside an Exchange server. OST files maintain an offline copy your Exchange server mailbox on your individual computer. OST files are optional. You can access all data from the Exchange server, but OST files provide faster data access.


As well as for day-to-day data storage, you can us PST files to export Outlook data for use on another computer. OST files allow you to access the most recently synchronized copy of your Exchange server data while not connected to your company network -- an invaluable feature for remote workers.