The tact and diplomacy of Mangammal helped in maintaining amicable relations with the neighbouring powers. She bought off the Muslims and was subordinate and loyal to them. She also bribed the Marathas. Mangamma successfully resisted the aggressive policy of Chikkadevaraya of Mysore. She undertook an expedition to Travancore to collect arrears of tribute. Her war with Tanjavur ended in peace and an alliance. In Ramnad, Kilavan Setupati was becoming more and more independent. In about 1698 A.D. he besieged Madurai city and took it but was soon driven out. In 1702 A.D. he became completely independent.
Mangamma showed great lenience towards Christian preachers and her Christian subjects. She was equally considerate towards other religions. A copper plate inscription of 1692 records a grant for the maintenance of a mosque in the name of her grandson. In 1701 she financed for the construction of a Muhammadan dargah as a gift to some villages near Tiru-chirapalli.
Mangamma has favoured many Hindus. Her liberality regarding charities and public works is proverbial. She is famous as a road maker. She built some artistic public edifices like summer house and the choultry, which is named after her prestigious name. She provided for the comfort of pedestrians by planting trees on the roads she constructed and repaired, and placing inns and supplies of water on the way. She made grants for providing village settlements for brahmanas called agraharas. An inscription of 1701 records a grant of land for a feeding institute. She paid attention to irrigation, as is indicated by her inscriptions on the bank of the Uyyakondan channel in 1687 and 1704. She is said to have met with a tragic death in 1706 A.D.