You can use a third-party programme like the Zimbra to Outlook Converter tool from KDETools.
A few characteristics are:
• This tool can convert files from Zimbra to Outlook as well as other file types including MBOX, MSG, EML, EMLX, PDF, HTML, etc.
• It extracts every piece of important mail details, including To, Bcc, Cc, Sent, From, Received, Attachments, etc.
• This utility quickly and without data loss converts Zimbra files to Outlook.
See More:
https://www.kdetools.com/zimbra/
