Preheat the oven to 350°F [180°C]. 

In a medium bowl, whisk together the mayonnaise and salt. Lay out a sheet of heavy-duty aluminum foil roughly 12 in [30.5 cm] square on a flat surface and place one salmon fillet in the center, skin-side down. Slather 1 tablespoon of the mayonnaise mixture all over the salmon, including the skin, coating the fish evenly. Return the salmon to the center of the foil. Lay a small bunch of dill sprigs on top of the salmon, and arrange 4 lemon wheels across the top in a line. Carefully fold up the edges of the foil to make a packet, and crimp the seams. (This will help keep the steam inside and keep the fish moist when cooking.) Repeat the process with the remaining salmon fillets. At this point the packets are ready to cook, but they can be stored in the refrigerator overnight.

Space the four salmon packets evenly on a large rimmed baking sheet. Bake for 20 minutes and remove from the oven. Immediately open each packet, being careful not to burn your fingers as the hot steam escapes. The salmon will easily pull away from the skin, if desired, or it can be carefully removed whole with a flat spatula. 

The salmon can be served hot right away, at room temperature, or cold. Sprinkle with chopped fresh dill and serve with lemon wedges.