What is the ruling on a suitor kissing his fiancée's mother on her cheek and head out of respect and appreciation for her?

The wife's mother is permanently forbidden (for marriage), and it is permissible to shake hands with her or kiss her head out of respect, provided there is no unnatural inclination. As for the fiancée's mother, she is considered a stranger (non-mahram), and it is not permissible to shake hands with her or kiss her.