Abstract: Apparatus for automatically opening and closing the flaps of a plurality of mailing envelopes. The apparatus includes means for forcing open flaps which have become stuck to the associated envelope body and has means for closing the flaps of such envelopes. Storage means are provided for handling envelopes in large volume and automatic feeder means are provided for feeding said envelopes into a flap processing section of the apparatus. Material flattening and ejection means automatically draw the processed envelopes through the feeder means and flap processing sections and eject said envelopes from the device by way of a conveying section after the flaps thereon have been processed.