Most other account types, such as IMAP accounts, Microsoft 365 accounts, Exchange accounts, and accounts use an Offline Outlook Data File (.ost) file to store a synchronized copy of your mailbox information on your local computer. When messages or other Outlook items are saved in an Outlook Data File (.pst), the items are available only on the computer where the file is saved. By moving items to an Outlook Data File (.pst) on your computer, you can free up storage space in the mailbox on your mail server. Note: You cannot import from an Offline Outlook Data File (.ost) file.īecause these files are saved on your computer, they aren’t subject to mailbox size limits on a mail server. For more information about importing items, see Import email, contacts, and calendar from an Outlook. You can also import email messages, calendar, contact, and task data from another Outlook Data File (.pst).

For more information on backing up your email messages, calendar, contact, and task data, see Export or backup email, contacts, and calendar to an Outlook. You can also use an Outlook Data File (.pst) to backup or export items from any type of email account. In Outlook 2016 and Outlook for Microsoft 365, IMAP accounts use Offline Outlook Data Files (.ost). Note: In Outlook 2013 and earlier versions, IMAP accounts also used an Outlook Data File (.pst). Tip: If your Outlook Data File (.pst) becomes large it can slow down your OneDrive sync and may show 'Processing changes' or 'A file is in use'.

Outlook drive