I’ve always learned that the article for Dativ Plural is den, for example
Ich kenne die Frauen, den man Bücher schenkt.
My Duden grammar agrees with me, but it is more common to see forms such as this:
Ich kenne die Frauen, mit denen er spricht.
My understanding is then that denen is the relative pronoun, and den is the article. Is this correct? Denen is new to me.