If you don't know how to import an Outlook PST file into Zimbra Desktop, use eSoftTools Outlook PST Recovery Software. Calendars, contacts, emails, tasks, notes, attachments, and other objects may all be recovered from PST files, and you can get a live preview of each Outlook item as it is changed by the software. MBOX, EML, EMLX, MSG, and HTML vCards are among the file types supported by this program. All users have access to the free demo version. You can recover up to 25 emails from each folder in the trial edition.

For more info:- Import Outlook PST File to Zimbra Desktop