BONUS: if you’re reading an email and you’re scrolling along with the space bar, and then you come to the end of the message so there’s nothing left to scroll, and then you press the spacebar again, the Mail program will jump to the next message. This works perfectly when your mail is sorted with the new stuff at the BOTTOM. It works in reverse if the new stuff is at the top. Try it and see.
Thanks to Dave for the bonus hint.