Perhaps change the message to something like: "Your account has been rate limited. For more information email [...]"
And honestly, having people beg via email is just gross power tripping behavior.
On the other hand, I'm not sure that it won't just make things worse, since not everyone is going to respond as well as you might to a message like "Your account has been rate limited."
Something I note having been caught up on both sides of this issue: as moderator and moderated.
HN itself is not one of the super-sites, but it is amongst the better discussion platforms on the internet here and now (boys), and has been for far longer than virtually any other instance I can think of (dating to 2007). Metafilter would be the principle other exemplar.
Usenet, Slashdot, Kuro5hin, Google+, Reddit, Ello, Diaspora*, Imzy, FB, Birdsite, and others, would be amongst the failures IMO. Not all are now defunct (though about half that list are), none remain usable.