That email was sent on January 19th, 2017.
Maddox's Kiwifarms thread was then a few months old, on page 17.
The "is he a lolcow?" debate was over and decided in the affirmative as it always seems to be and people were just having a good natured laugh about Maddox picking the wrong side in the culture war and how he was generally acting like a weirdo by suddenly ending his podcast, refusing to explain it to his fans and blocking people who asked him about it.
But funnily enough, the day before that email was sent, Null's first appearance on The Dick Show had been posted on Kiwifarms.
Joshua "Null" Moon, owner and administrator of Kiwi Farms, makes his appearance on Episode 33 of The Dick Show, "Dick on Shaved Ice". #TheDickShow #KiwiFarms #Null #...
clyp.it
It's an entertaining listen even though we've probably all heard it before.
In the interview, Dick mentions that Maddox has a thread in "a section of something called
lolcows" and encourages people to check it out.
The very next day, that threatening email goes out.

Maybe that shit had been going on for a while, I don't know and am not going to go back and check.
But if that was the first example of restraining-order tier harassment sent to 80s, then did Maddox take the promotion of Kiwifarms on The Dick Show as Dick fighting dirty and decide "all bets are off now - time to call up my bottom bitch janny"?
We know that the Kiwifarms involvement was a significant thing to Maddox as he included lots of screenshots of it in his lolsuit.
Another interesting thing: the day after that email was sent, Asterios makes his first appearance on the Farms.