OST files: what are they and how do I open them?
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Microsoft Outlook inbox off-line folder
An ost file extension is used for Microsoft Outlook Offline Folders files. The ost files are used to store e-mail messages and other data download from an Microsoft Exchange server. Microsoft Outlook Offline Folders files are very similar to Outlook personal folders files (.pst files).
Further details:
The ost file extension is associated with Microsoft Outlook, a personal information manager, which is part of Microsoft Office, developed by Microsoft Corporation.
The ost file stores e-mail messages and other data saved by the application from an Exchange server.
The ost files are very similar to the *.pst personal folder files, but do not support large file sizes.
The ost files are created when the "Use Offline Folders" option is checked in Outlook and are stored on the hard drive instead of the e-mail server.
Default location of ost files is:
Windows Vista, Windows 7, Windows 8, Windows 10
\Users\user\AppData\Local\Microsoft\Outlook
Windows XP or Windows Server 2003
\Documents and Settings\user\Local Settings\Application Data\Microsoft\Outlook
Open file with:
Microsoft Outlook
An e-mail management tool distributed with Microsoft Office suite
Microsoft Outlook for Mac
Mac version of the popular e-mail client and personal information manager from Microsoft