Removable stacking device for automatic mail sorting machine

Removable stacker for an automatic mail sorting system comprising a flat rectangular plate defining a stacking area, a mobile wall at right angles to said plate and movable across the plate in a direction of a stacker inlet at a edge of the plate and adapted to contact documents on edge on said plate, a return device operatively coupled to said mobile wall for moving said mobile wall in a direction opposite to the direction of movement of said documents as the stacker is filled from the stacker inlet toward the mobile wall, and an articulated flap coupled to said plate and pivotable between a first position in line with the plate to a second position at right angles to the plate and closing off said inlet and for contacting a stack of said documents to an opposite side of a stack of documents from that of said mobile wall to grip said documents during manipulation of the removable stacker, and said stacker further comprising means for maintaining said flap in said second position against the action of the weight of the stacked documents pressed against the flap by said return device acting on said mobile wall.