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.OST File Extension

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Outlook Offline Folder File Icon
File TypeOutlook Offline Folder File
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Rare Uncommon Average Common Very Common
CategoryMisc Files
File Format Description

Stores e-mail messages and other data saved by Microsoft Outlook (2005 or later) from an Exchange server; similar to a Personal Folder (.PST) File, but supports larger file sizes.

OST files are created when the "Use Offline Folders" option is selected in Outlook and are stored on the local hard drive instead of mail server.

Program(s) that open .OST files
Updated 5/4/2015