Originally Posted by
Often1
If DL sells the connection, it is within MCT. If it is within MCT, the bags can be transfered.
Needless to say, the MCT does not account for delays in your arriving flight nor any delays which you or your bag may encounter at CBP.
Outgoing checked bags on a domestic to international connection shouldn't be subject to CBP, although there might be an exception if there's a suspicion that the bag contains more than $10,000 in unreported cash and cash substitutes (which would be a Treasury regulation violation IIRC). Otherwise, AFAIK customs has nothing to do with stuff leaving the USA, just incoming (checked and carry on) bags but maybe drug smugglers are an exception. Some countries such as Russia do an outgoing customs check but the USA does not.