Is the son of the wife's sister from the mother considered a forbidden relative to her, and is it permissible for her to shake his hand?

The son of a full sister, or a sister through the mother, or a sister through the father, is a mahram (definition) to a woman, based on the Almighty's saying: "Forbidden to you are your mothers, and your daughters, and your sisters, and your paternal aunts, and your maternal aunts, and your brother's daughters, and your sister's daughters." The mahram relatives are seven: the mother, the daughter, the sister, the paternal aunt, the maternal aunt, the brother's daughter, and the sister's daughter. It is permissible to look at the maternal aunt and enter upon her even without another mahram present, as long as the situation is normal among people, free from temptation and doubt, based on the Almighty's saying: "And let them not expose their adornment except to their husbands, or their fathers, or their husbands' fathers, or their sons, or their husbands' sons, or their brothers, or their brothers' sons, or their sisters' sons." Shaking hands with the maternal aunt and other mahram relatives is permissible and there is no harm in it if temptation is secure.