Here's what I found in a security brochure for Canon MFPs:
Mail box imageRUNNER ADVANCE systems offer an onboard secure printing workflow. For example, a user can store print jobs to a password-protected Mail Box on the device. Later, that same user can walk up to the device and enter the Mail Box password to print the job as needed.
Advanced Box is the collaborative storage space on imageRUNNER ADVANCE systems. Advanced Box enables users to store electronic files within a multitiered folder structure. Folders may be password protected to protect document access. Both native and printable files are accessible from PCs. Printable versions of files are accessible directly from the User Interface at the device.