It was authentically reported that the Prophet (peace be upon him) said: I do not shake hands with women.
Moreover, `Aishah (may Allah be pleased with her) said: The hand of Allah's Messenger (peace be upon him) never touched the hand of any woman, but he only used to take their pledge of allegiance orally.
More disgraceful than shaking hands with nonMahram women is kissing them, whether they are paternal or maternal cousins, neighbors, or fellow tribeswomen. Such a practice is prohibited according to Ijma` (consensus of scholars). Moreover, it is one of the greatest reasons leading to adultery.
Thus, it is obligatory for a Muslim to be on his guard against it and to convince all his relatives and other women, who are accustomed to doing such a practice, that it is prohibited. It is not permissible for a Muslim, male or female, to participate in such behavior even if it is a widespread custom among relatives or fellow citizens. Rather, they should deny such a practice and warn their society against it. Anyway, it is enough to greet someone verbally without shaking hands or kissing.