I mailed Arnold a SASE, LOR, photo on January 1st, 2019 and received it on February 15, 2019
I received a pre-print photo back, with my enclosed also included. There was small leaflet explaining that this address is not for fan-mail and that Arnold is too busy to sign anything. However they did appreciate me writing out to him.
The address I used is
Arnold Schwarzenegger
P.O. Box 1234
Santa Monica, CA 90406
USA
I unfortunately already got rid of my envelope so I can't get a picture of it
2020 Received: Weird Al
2019 Received: David Anderson (Canadian MP), Eric the Car Guy, Chrisfix, Jay Leno, Arnold Schwarzenegger (PP), Jonathan Banks, Hickok45, Bob Gale, Jimmy Carter, Jason Kenny (politician)
2018 Received: Seth MacFarlane, Creed Bratton, Nancy Cartwright (bookmark), Scott Moe (politician), Andrew Scheer (politician), Tim Allen, Chris Pratt, Jennifer Lawrence, Eric O (South Main Auto), Johnny Depp (gifted to a friend), George W Bush (photo print)