A sheet media handling system is provided for use in a sheet processor (e.g., a printer). Such system incorporates an input tray for storing one or more sheet media prior to input through the printer's input port with the input tray vertically stacked with the printer's output support structure or tray. The system also has a single sheet medium guide mechanism adjacent the printer's output support structure, where the medium guide mechanism routes a single medium to the input port when the single medium is inserted therein. The single sheet medium guide mechanism includes a skew-abatement substructure and a deflection mechanism. The skew-abatement substructure is designed to facilitate alignment of and routing of a single medium towards the input port by contacting a first edge of the single medium and an opposite second edge of the single medium. Such a deflection mechanism is designed to deflect a single medium toward and into the input port by contacting the upper surface of the single medium while also contacting the lower surface of the single medium. The invented system facilitates easy manual insertion and alignment of a single medium (e.g., an envelope or postcard) into the input port of a printer without affecting the existing supply of sheet media in the input tray.