Cook macaroni following directions on the package. Drain into a colander and rinse with cold water. Cool to at least room temperature, or in the fridge.
Meanwhile, in a large bowl combine celery, onion, relish, eggs and peas.
Stir in cooked macaroni.
Stir in mustard and mayonnaise and blend thoroughly. Taste and add salt as desired.
Store in a tightly sealed container for up to 5 days. If salad seems dry, add a couple of tablespoons of mayonnaise to moisten.
Notes
How to Store Leftovers: Store macaroni salad in the refrigerator in a tightly sealed container for up to 5 days. If the salad seems dry, add a couple tablespoons of mayonnaise to moisten it before serving.