Preheat oven to 325 degrees F (165 degrees C).

Stir boysenberry syrup and Dijon mustard together in a bowl until glaze is well-combined.

Place ham, cut-side down, on a rack in a roasting pan. Generously brush about 1/2 of the glaze over the ham and cover ham loosely with aluminum foil.

Bake in the preheated oven until almost completely heated through, about 3 hours. Remove and discard aluminum foil, brush ham with remaining glaze, and continue baking until ham is completely heated through, 25 to 30 minutes more.