The best Software Solution to back up Office 365 emails is the MacSonik Office 365 Email Backup Tool. The program allows you to export Office 365 Mailbox to PST, MBOX, EML, & CSV file formats on macOS.The tool easily migrates or exports data from Office 365 to multiple cloud servers such as IMAP, and Office 365. Moreover, it also offers a Mail filter & task filter option to download Office 365 Mailbox to PST from a specific date range.