I would LOVE to know how they managed to destroy numerous emails on numerous computers without throwing the hard drives thereon into the Potomac. But since this report comes from Waxman, I am not sure they did.
Simple. Until someone brought it to their attention, the RNC didn't have a "keep it forever" mail retention policy. Some messages expired and were thus deleted.
The White House email system, the one they're supposed to use to ensure compliance with the law, never deletes, or allows a user to delete, anything.