You need to think outside the envelope

This happened during a discussion regarding thinking more creatively. It is a mashup of “think outside the box” (think freely, not bound by old rules or practices) and “push the envelope” (to surpass normal limits or attempt something viewed as radical). Maybe putting an envelope in a mailbox caused the confusion? Or perhaps it is because both idioms involve a thought or action beyond the norm. In any event, this nice malaphor was sent in by Dave Nemcsik. Thanks Dave!