USA Customs and Immigration Information connecting flights.

Hi,
Flying vs to jfk with onward delta flight to San Juan Puerto Rico. I understand that on the outbound flight I have to collect my bags at Jfk and re check them in for the onward delta flight to sju.
My question is do I have to do the same on the return flight or will my bags be tagged at sju to pick up at Heathrow.
Thanks

No, as it's a Domestic to International connection you don't even have to re-clear security as long as you have your onward boarding pass and bags are tagged through.

Thank you. Will help decide on flight times.