An apparatus includes an input bin for receiving a stack of envelopes, a conveyor for conveying each envelope of the stack along an envelope path, and a cartridge retainer adapted for electrical connection to an inkjet cartridge defining a 1×M array of inkjet printing nozzles. The apparatus further includes a controller electrically coupled to the cartridge retainer and configured to activate the inkjet cartridge nozzles to deposit ink droplets according to a predetermined duty cycle able to cause printing, on an envelope conveyed at a first feed rate, a first indicium having a density of M×N dots per inch, where N is greater than M/2 and less than M. The conveyor, however, conveys envelopes faster than the first feed rate, whereby the first indicium is printed at a density of less than M×N dots per inch on a moving envelopes.