Add the dill, mustard and capers to the mayo. Squeeze in some lime or lemon juice, to taste. Start out with a small amount and go from there.
Mix all dill dip ingredients very well. Season with salt and pepper, to taste (if needed).
Serve with chips, crackers, celery, zucchini and carrot sticks, or whatever you like dipping with. You can also serve it as a sauce over salmon.
Notes
Cover the dip and store in the fridge for up to 3 to 4 days.
I do not recommend freezing the dip. The ingredients may split when thawed due to the mayo. If you do freeze it, thaw it in the fridge and stir really well before serving.