The personal mailbox is the mailbox you use on a daily basis, while the system mailbox is used by your team for receiving candidates application and sending automatic emails to them (it is usually [email protected] or [email protected]). You can assign a number of users to an integrated system mailbox. 

NOTE: when you send messages to candidates from Traffit your personal mailbox is used by default. Mailbox creation and management is on your company end, Traffit is only responsible for its integration with the system.