In a large bowl, mix mayonnaise, sugar and vinegar until well blended. Stir in buttermilk, caraway seeds, mustard, horse radish, pepper and salt. Add cabbage and toss to coat. (can be prepared 3 hours ahead. Cover and refrigerate.) Substitute for buttermilk: Put 1 Tablespoon of either lemon juice or vinegar in a measuring cup. Add milk to make 1 cup. Let it sit for 15 minutes.