 If printing is required on all four flaps as well as the front, the process is referred to as "printing on the flat".Eye-catching illustrated envelopes or pictorial envelopes, the origins of which as an artistic genre can be attributed to the Mulready stationery – and which was printed in this way - are used extensively for direct mail.In this respect, direct mail envelopes have a shared history with propaganda envelopes (or "covers") as they are called by philatelists.