Abstract: The invention concerns sealed mailer assemblies including return units made from individual sheets in a single production line and a method and apparatus for forming them. The sheets have their longitudinal edges glued and are then formed with a plurality of transverse folds so that the adjacent parts of the longitudinal edges are all secured together. The free transverse edge is also glued down. Tear lines are formed within the glued edges so that on removal of the edge portions several separate pieces are provided. An ink jet printing unit is provided within the production line capable of forming accurately positioned personalized information on any data carrying part of each sheet.