There are mainly 3 thing which you should be careful to ensure a long shelf life of your pickle-
1-first and foremost , you have to wipe and dry the mangoes very thoroughly,even the slightest bit of water or moisture in mangoes or in the storage jar is enough to form fungus and mold and ruin your pickle.
2-The amount of salt should be measured accurately as it act as a preservative for the pickle.
3-The pickle should be covered with a layer of oil all the time.
4-Occasionally keep the pickle jar in sunlight for few hours.