In a large bowl, stir together the mayonnaise, mustard, vinegar, sugar, salt, onion powder, and celery seeds. Add the shredded cabbage and toss until well coated.
Refrigerate for an hour before serving and up to 2 days. Toss again right before serving.
Notes
Finely shredded cabbage may be substituted for the store-bought coleslaw mix in this recipe.