Import messages saved in an offline Outlook Data File (.ost)

Offline Outlook Data Files (.ost) are used with email accounts where your mail is kept on a mail server, but a local copy of your messages is saved and synchronized on your computer. Microsoft Exchange, Outlook.com, and IMAP accounts are examples of accounts that use an offline Outlook Data File (.ost).

These files improve performance and allow you to continue to work with your email even when your computer can’t connect to the mail server.

Because the contents of offline Outlook Data Files (.ost) are copies, you don’t need to back up the file. If you replace your computer or begin using another one, add your email account to Outlook. A new offline Outlook Data File (.ost) is created and a new copy of your messages is downloaded.

Outlook doesn’t support importing messages from an offline Outlook Data File (.ost). We also don’t recommend you manually move the existing data file to another computer. On the other computer, add your email account to Outlook. A new offline Outlook Data File (.ost) is created and copies of your messages are downloaded.

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