Reactive Training Systems

You can use third party application like KDETools Zimbra to Outlook Converter tool.
Several features are:

• This application also convert Zimbra files to Outlook and additional file formats such as MBOX, MSG, EML, EMLX, PDF, HTML, etc.
• It extracts all the necessary mail data like To, Bcc, Cc, Sent, From, Received, Attachments, etc.
• This application easily convert Zimbra file to Outlook without losing data.

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