Not an email. A real postcard, with a real stamp, sent from wherever the boat happens to be docked. Drop your address below and get in the pile. Leave a note if you want something to react to.
Sent whenever he gets around to it. That is the whole promise.
A postcard takes as long as the mail takes. A Cameo shows up in days: birthdays, roasts, pep talks, whatever you need him to say on camera.