Let the ham sit at room temperature for 30 minutes to 1 hour. Preheat the oven to 325 degrees F. Trim off any skin from the ham. Score the ham in a diagonal crosshatch pattern (about 1-inch apart) without cutting through into the meat. Place the ham, flat-side down, fattier side up, on a rack in a roasting pan. Pour a 1/2-inch of water in the bottom of the pan. Cover with aluminum foil and roast, about 1 hour. Remove the foil, add more water if the water has dried up and recover loosely with the foil. Continue to bake until the ham reaches 130 degrees F, adding more water if needed to keep the roasting pan from burning, 1 hour to 1 1/2 hours more (about 15 minutes per pound).
Increase the oven temperature to 400 degrees F. Whisk the marmalade, mustard, brown sugar, vinegar, coriander, ginger, allspice and a generous amount of black pepper in a liquid measuring cup. Spoon off about 1/4 cup of the pan juices from the ham and whisk into the glaze mixture. Brush about half of the glaze all over the ham. Continue to bake, brushing the ham with the glaze twice more until the surface of the ham is caramelized and the internal temperature in the center of the ham reads 140 degrees F on an instant read thermometer, adding more water if the bottom of the pan dries out and begins to burn, 40 to 45 minutes. Transfer the ham to a cutting board or platter and let rest for 20 minutes before slicing. Serve with the rosemary, oranges and any additional glaze on the side.