Combine peaches and a splash or two of water in a high-powered blender. Blend until smooth.
In a large cocktail shaker (or working in batches as needed), combine 4 ounces of the peach puree, mezcal, triple sec, lime juice, and simple syrup. Place the lid on the cocktail shaker, and shake, shake, shake.
Dip each glass in a combination of Tajín and margarita salt. Fill each glass with ice and then pour the margaritas. Enjoy immediately!