To make the simple syrup, combine the granulated sugar and water in a small saucepan and bring to a boil. Cook until the sugar has completely dissolved. Let cool.
Meanwhile, cut the mangoes and place the flesh in a blender or food processor.
Add the salt and lemon juice, then blend until smooth and creamy.
Strain the mango purée through a fine-mesh sieve.
Stir the cooled simple syrup into the mango purée.
Refrigerate the mango purée for 12 hours.
At the same time, place the ice cream maker bowl in the freezer for 12 hours.
Pour the mango mixture into the ice cream maker and start the machine. Churn for about 20 minutes, following the manufacturer's instructions for your ice cream maker.
Serve immediately or transfer to an airtight container and freeze for up to 1 month.