I would like to suggest gainful software like KDETools Zimbra to PST converter. This application simply convert Zimbra file to PST without any hassle. This application has batch conversion option to convert multiple Zimbra file to PST. This application easily convert Zimbra to MBOX and multiple file formats such as MBOX, OLM, EML, EMLX, HTML, and etc.
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https://www.kdetools.com/zimbra/