That's email seems oddly targeted towards an insecurity that most trolls wouldn't bother poking at, and seems needlessly harsh to boot.
If this email is authentic, I suggest disregarding it. I know it's easier said than done, but, some people will never be happy. Invest your time and emotional bandwidth on causes that matter to you, or otherwise aren't lost.
Rationally I understand that people such as this sender are not representative; most individuals who bother to contact us have only kind and/or constructive things to say. But over the years these isolated haters have dumped a lot of their bile onto me, and it's hard to resist the corrosion indefinitely.
That being said, posting that nasty email here is part of my strategy for maintaining a rational view of it. It's less destructive out in the light.
If this email is authentic, I suggest disregarding it. I know it's easier said than done, but, some people will never be happy. Invest your time and emotional bandwidth on causes that matter to you, or otherwise aren't lost.