There are many scenarios where the currently-highlighted message is not the first message (as sorted by date) for the selected account. The only way I’ve found to get back to the top (first) message is by grabbing the scroll bar and manually sliding it to the top.
A toolbar button and/or a keyboard shortcut option would be most helpful.
“If you have eM Client for Windows, you can press the “Home” key to automatically go to the top” of the message list.
“If you have Mac and “no Home key”, then It’s Fn left arrow to go to the top of the list.
“Most full-size Mac Keyboards have a Home button so you can also use that”.
Thanks! [Home] key does exactly what I want. I don’t see that on the list of keyboard shortcuts. (too obvious, maybe? 
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Yes i don’t know if it is officially documented, and only that @Gary advised that in a post years ago.
You can also use the “End” key to go to the bottom of any email list as also posted by Gary.
And it turns out that PageUp and PageDown also work as expected! Nice, nice and double nice.