You can use the Zimbra to Outlook Converter tool to convert Zimbra files to Outlook without losing any data.

• Throughout the conversion process, the folder structure is preserved by Zimbra Converter.
• Various file formats, including PST, MBOX, MSG, EML, EMLX, PDF, OLM, and HTML, are supported by Zimbra converter.
• Cluster change is upheld by this application.
• It extracts every essential piece of mail data, including To, Bcc, Cc, Sent, From, Received, and Attachments, among others.

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