Reference: Fataawa an-Nadthar wal-Khulwah wal-Ikhtilaat – Page 11
Question: Some men shake hands with female relatives who they are not mahrams to, rather because they are relatives or neighbours. What is the ruling for that?
And is it sufficient for the women to place a piece of material on their hands intending to cover it?
Response: It is not permissible for a man to shake hands with a woman [to whom he is not a mahram], even if she put a piece of material on her hand whilst shaking hands.
And with Allaah lies all success and may Allaah send prayers and salutations upon our Prophet (sal-Allaahu ‘alayhi wa sallam) and his family and his companions.