Mix mustard, salt, pepper, egg and 1/2 cup mayonnaise. Add sweet peppers and crab meat and mix lightly, being careful not to break crab lumps. Pile in ungreased baking dish. Top with a light coating of mayonnaise and bake in oven at 350 degrees for 30 minutes. Serves 4. (May be baked in individual casseroles for 15 minutes.