A dynamic "mailboxing" unit and system for separating by users the sheet outputs of various users of a shared users printer (including facsimile receivers, copiers or combination units). It provides for stacking the sheets sequentially outputted from the printer in separate job sets into one or more temporarily and variably assigned "mailboxes" of a "mailboxing" job sorting accessory unit. The "mailboxing" unit has locking "privacy doors" for restricting access to at least some of the mailbox bins, with electrical unlocking of selected bin doors in response to entry of a user access code, and in particular, automatic lifting of one edge of the sheets in that bin in coordination with the bin door opening to assist user removal of their sheets from the bin.