It doesn't "drop" them. It puts them on hold, on ice, so to speak. Then the list manager has to go in and initiate a reconfirmation, or the one who has been put on hold has to log in and initiate one themselves (they can do it themselves). Yahoo does get sticky about bouncing addresses. But they are not banned, just blocked until the mail works again (and has been confirmed to do so). Daniel Diane Fields wrote:
Message
Re: [QuadtoneRIP] banned/blocked
2005-04-27 by Daniel Ridings