In my usual review of email, I have the message preview pane open and use the keyboard to delete, archive, or skip messages with the focus in the message list. Sometimes I want to click a link in in an email. When I'm finished with that, I usually switch back to Mail using ⌘-Tab. In that case it takes a mouse/trackpad gesture to put the focus back in the message list. Normally, I would expect to be able to use ⌥-Tab to shift focus between the panes, but instead, the focus moves to individual items in the toolbar and skips the message list. What am I missing?
You can enable Favorites bar where each element has shorcuts like ⌘1, going from 1 to 9. When you keystroke shortcut of an inbox its message list gets focus.
If you have multiple mail accunts you have to use corresponding shortcut for each inbox. This is not as ergonomic as a single shortcut would be though.
I've recently discovered that you can shift focus from a message to the message list with an awkward combination of two repetitions of ⇧⌥-Tab then ⌥-Tab. I.e. you can't "back up" to the message list; rather, you have to shift focus to it in the "forward" direction. It seems like there should be a better way to do this in a single keystroke. If anyone knows a better keystroke or shortcut, I'd love to hear it.