A MarketingProfs column explains the pitfalls of co-registration deals - where companies build their own email lists through other lists that offer incentives to get subscribers to opt into the marketer's email program. Of course, with this sort of deal, there is great potential to get bad data or lists of names that didn't really intend to opt into the marketer's list. Marketers can engineer insertion orders to include provisions protecting from some of the worst of the bugaboos.