A mechanism is described for automatically handling envelopes and paper sheets, the mechanism having an input window for receiving the envelopes and paper sheets. The mechanism comprises a first tray for holding a stack of paper sheets and is mountable in the window. A second tray is provided for holding a stack of envelopes and is also mountable in the window. A roller system is positioned to selectively engage the topmost sheet of the stack of sheets in the first tray or a bottommost envelope of the stack of envelopes in the second tray and to feed either the topmost sheet or the bottommost envelope, as the case may be.