For me one of these sorts of situations, it got so bad I started cancelling flights and hotel reservations as they came in. That gave the person who had the errant email address enough incentive to actually fix it.
Oh we were nice enough about it, we even tracked down what the person's "actual" email address was and tried to get them to change it. They not only were they unwilling to fix it with the places they had given it out they added more. So it wasn't like they felt compelled to be helpful. And of course it isn't really possible to "junk" emails from legitimate businesses to your email that you might want to do business with at some point.
