Argh, this has been frustrating for two years, I've looked and looked for the Superhuman commands that would take you to the very top of a mailbox or to the very bottom and nothing seems to list it. But finally, I had the inspiration to just try the Vi equivalent command which are
gg to go to the very top and G to go to the very bottom and this worked!
Unfortunately, doing 10G does not get you to the then 10th mail, but I wish it did. Ok, I'm a nerd for wishing that all the vi commands would work with Mail, but I guess I'm too old to learn differently I love vimari for that reason (add vi movement to Safari), Jupyter vi-mode as another example 🙂
Note that regular
g will help you to get to various splits that is
gi means go to inbox and so that's the way to get to the top (most recent message of the inbox), but the double gg command is a vi-ism. Also I love their use of j, k to go through email and n and p to move through a thread. There was an old project to let you use those keys for Mac Mail called HJKL (you get it if you look at the keys on your computer), but it hasn't worked in seven years 🙁
And a true power nerd can use notmuch to download mail and read it in vim. Yikes that sounds pretty terrible as an interface, but you can do that and also use vi with a calendar.