Peel the mangoes and cut them along the stone. Dice the pulp. Wash the limes with hot water and pat dry. Rub 1 teaspoon peel, squeeze out the juice.
Puree two thirds of the mango cubes together with the lime juice in a blender. Mix the mango puree with the remaining mango cubes and place in a saucepan with the lime zest and sugar. Bring to the boil while stirring. Then do a gel test. Pour the jam into jars rinsed with hot water and close tightly.