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Export mailbox as a PST file Login to Outlook with the Exchange account that was used to create the OST files. And to export the OST mailboxes to PST, follow the simple procedure as given here:
Go to Files >Open & Export and click Import & Export.
Select Export to a file; then click Next.
Select the second optionOutlook Data File (.pst)and click Next.
Select the folder(s) which you want to export and click Next.
Browse the location where you want to save the new PST file 5. and choose an option regarding the duplicate items.