I honestly skip the whole j key crap in TB wherever I can; No need for it.
I just highlight the message(s),
Shift+F10/Applications,
k to Mark Message As,
j for Junk
(or n for Not Junk).
I intentionally put Shift+F10 first because all/if not most keyboards are increasingly dropping the Applications key (something that slows me down a fairly unnecessary bit?).
That's why I miss the true business laptop that pulls a Listerine (says what it does, does what it says)?

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Jason Bratcher