Soak the cedar plank for 1 hour in cold water to cover.
Make the glaze: Place the mayonnaise, mustard, dill, and maple syrup in a mixing bowl and whisk to mix.
Drain the cedar plank and dry. Arrange the salmon fillet on top and season generously on both sides.
Place the plank with the salmon on the grill over the drip pan. Indirect grill the salmon until the glaze is puffed and browned and the fish is cooked through, 20 to 30 minutes. Use an instant-read meat thermometer inserted through one end to check for doneness: the salmon should be about 130 degrees.
Transfer the plank to a heatproof platter and serve the fish right off the plank