>You can be damn sure the government has a list of possible email addresses associated to individuals.

things the government knows, and things that a CBP agent knows, are not the same thing. They NSA doesn't just provide their database to all the hundreds of thousands of front-line law enforcement agents. If you're being specifically targeted for some reason, enforcement agencies might be provided with a history of your social media activity, but it's unlikely that they can just pull it up when they type in your drivers license number.