One or two inches of mulch spread on the soil's surface around mango trees (but not touching the trunk), is usually beneficial. But there is a possibility, not at all well studied, that mulch made from a particular kind of tree, could retard growth.
Mulch, compost, and highly organic-matter potting soils, when placed down in the planting hole are usually harmful. They gather and retain too much water, even with well-drained sandy soil around the planting hole.