Office 365 - Apple Mail - Exporting a Mailbox
This document will provide step-by-step guidance on how to export a mailbox from Apple Mail.
Open the Mail application.
Right-click on the folder you want to export, then select Export Mailbox...
Select a location where you would like to save the exported mailbox. Then click Choose. A .mbox file will be created and stored in the location you selected.
You now have a copy of the Apple Mail mailbox you selected.