"I get mail from all over the world, 122 countries," she told CNN.
Henderson, 75, played Carol Brady for five years but the show has remained on TV in syndication, and generations of children have grown up with the Bradys.
Recently, Henderson became the spokeswoman for the "Center for Lackus Appreciatus Prevention," part of a Kodak promotion for online Mother's Day cards. She said many mothers suffer from "a condition caused by years of under-appreciation and neglect" by their children.
Henderson has also been touring in her one-woman show, "All the Lives of Me."