Just install and launch the software on your system.
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In this step, add PST file on the home screen of the software.
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Check PST mailbox preview and hit Export button on the top-right of the screen.
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Select MBOX format and hit Browse button to provide a location for saving Postbox MBOX files.
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In the end, hit Convert Now and within a few minutes, conversion of PST mailboxes to Postbox gets completed.
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