The original source was the New York Observer. They're owned by close Trump confidante Jared Kushner. At least according to the Observer, and they're close enough to Trump to know, it at least appears to be legit.
Trump's most ardent supporters would like to shout down any not-so-flattering reports about him as "fake news." Normally I'd say that this kind of story, without any real proof, could easily be fake, but much to my surprise, from everything I can find about the author (Sage Lazzaro), she typically likes to write clickbait but not anything hoax-like.
I personally don't think it's real:
1) she won't publish the letter
2) Trump's legal team has defended the guy for years. They know if they denied sending a letter and then she was actually able to produce the letter it would make them look very stupid.
3) The domain name stuff really puts the claim in doubt, IMO
4) Twitter is filled with way worse photoshops of Trump. Trump would need to sue literally millions of people.
5) Trump is a public figure and knows this stuff is futile.
6) It would look horrible. People already think Trump is a dictator, rightly or wrongly.
7) I doubt they would have even noticed this.
And so on and so forth. Of course, the problem with claiming everything is "fake news" is that when something actually is fake news, people believe it.
