Abstract: An unflapped envelope (60) is fed, with its crease line trailing, along a path (42) from an envelope feeder and between the rollers of a reversibly driveable roller pair (43), for onward transfer to, for example, an insertion station. When the crease line reaches a predetermined point in front of the roller pair (43), the drive is reversed and the envelope with the crease line leading directed along a flapper path, including a deflecting surface 46, to a flapping chamber or zone (47), at least until the flap (61) is engageable by flapper blade means (44;44a). The drive is then reversed again and the envelope driven back along the flapper path, a flap opening surface (49) of a flapper blade (44) or a pair of flapper blade elements (44a), causing the flap (61) to be stripped from the body of the envelope (60) as it exits the flapping zone, and proceeds to the insertion station.