Manually, you can use the eDiscovery tool to take the backup of Office 365 mailbox. You can configure Office 365 in Outlook and create the backup in the PST file format. Alternatively, to export Office 365 mailbox to PST there is one more option; one can use the software to save Exchange Online mailboxes data. There are a few reasons people look for third-party solutions or Office 365 Backup software but I suggest you try the manual process first. If I talk about software, you can try MailsDaddy Office 365 Backup Tool. As it is a perfect software to give you the complete solution to backup single or multiple Office 365 mailboxes. Through this application, you can easily create a backup of Office 365 including Exchange emails, calendar, contacts, notes, etc. It also allows backing up contacts or calendars individually.