Coat beef brisket with mustard. Cover with brisket rub. Let marinate in the refrigerate, 8 hours to overnight.
Remove brisket from the refrigerator and bring to room temperature.
Preheat a smoker to 220 degrees F (104 degrees F) according to manufacturer's instructions.
Place beef brisket in the smoker and smoke until easily pierced with a knife and an instant-read thermometer inserted into the center reads 190 degrees F (88 degrees C), 6 1/4 to 7 1/2 hours.
Wrap brisket with aluminum foil and let rest for 30 minutes before slicing.
