Dijon mustard counters the sweet maple syrup and apricot jam, giving this ham a more nuanced flavor.
Preheat oven to 350 degrees. Place ham on a roasting rack in a large roasting pan. Cover tightly with foil. Bake, rotating pan halfway through, 4 hours.
Meanwhile, make glaze: In a small saucepan, heat jam until liquefied. Strain through a fine sieve into a small bowl; discard solids. Stir in mustard, maple syrup, rum, and garlic.
After 4 hours, remove ham from the oven, and brush with glaze. Continue baking the ham, glazing every 15 minutes, until an instant-read thermometer inserted into thickest part of the ham (avoiding bone) registers 140 degrees, about 1 hour more. Remove from oven, and transfer to a carving board or platter. Garnish ham with bay leaves and kumquats, if desired. Slice thinly around the bone, and serve hot or at room temperature.
One to two hours before baking, remove the ham from the refrigerator and let it come to room temperature.