You can use a third-party application like KDETools' Zimbra to Outlook Converter to import Zimbra into Outlook.
Some features include:

• In addition to Zimbra files, this application can import MBOX, MSG, EML, EMLX, PDF, HTML, and other file types into Outlook.
• It extracts every necessary piece of mail data, including the To, Bcc, Cc, Sent, From, Received, and Attachments, among others.
• Without losing any data, this program makes it simple to import a Zimbra file into Outlook.

More details: https://www.kdetools.com/zimbra/