602dn has 5-bin mailbox.
5-bin mailbox work in "Mailbox" Operation Mode.
After firmware update (2302243_421978 22 Nov 2013), if I print to "first mailbox bin" - printer showing error "please, open rear bin". Print to 2-nd, -3,-4,-5 mailbox bins are fine. Error only at 1-st bin of mailbox.
Please check and fix firmware.