If you want to take a backup of your Office365 Mailbox in Mac OS. You can use Mac Backup office 365 tool, this software quickly works on Mac OS. And it enables you to backup Office 365 emails, contacts, and calendar to PST, MSG, EML, EMLX, and MBOX. The application gives only a few easy actions to achieve the conversion from Office 365 folder to the required format in any single and bulk mode just a few minutes. The software supports all versions of Mac OS like (10.11).
For more information: toolscrunch.com/mac-office365-backup.html