Writing "Kind regards" is one of the standard ways to end an e-mail and therefore it is not overly personal. I have seen "Kind regards" used in business e-mails when the people know, don't know or hardly know each other. You can also use "Kind regards" in private e-mail. However, when I send e-mail to someone who is
very close to me (my husband, children or best friend, for example), I normally would
not use "Kind regards".