Abstract: An upright, generally cubicle sheet metal mail sorting rack for at least temporarily storing a plurality of trays filled with items of mail. Each cabinet comprises a pair of rigid, spaced apart end panels of generally rectangular dimensions. A plurality of vertically spaced apart retractable shelves are supported within the cabinet between the end panels by a dynamic mounting system. The shelves can be manually displaced from a retracted within the cabinet to an extended, tilted position facilitating tray access. The mounting system comprises a pair of segmented tracks for each shelf, and suitable wheel bearings which ride upon the tracks. Each segmented track comprises separate horizontal and angled track members mounted on the interior of the cabinet end panels. Pairs of wheel bearings project outwardly from each shelf end; front wheel bearings ride on the horizontal track and the rear wheel bearings ride on the angled track.