If find it a bit odd that:
a) It's not a signed for or otherwise recorded letter. I can't speak for the US, but here in the UK legal documents like that are hand delivered by either a courier, the police, or other such legal personnel, and you always have to sign for them.
b) It's sent as an email to an address that may not be monitored, may have such emails filtered as spam or probably gets hundreds of spam emails every day making any real emails hard to spot, may not have all emails read if it gets a lot of traffic, yet it threatens legal action in two weeks on the assumption he will actually have read it. I doubt that's enforceable.
c) It's not sent from their US headquarters which are just along the road from the guy, but from Taiwan.
d) Despite being sent from Taiwan, it's written in very good English.