The problem goes back to the early days of the Internet when SMTP (Simple Mail Transfer Protocol) was defined.  The "to:" and "from:" fields are actually data in a mail message, not handshake stuff.  I use to fry peoples minds that didn't believe me by sending them e-mails that appeared to be from "Your Mother" or "GOD".  Thus its absolutely trivial to fake where an e-mail comes from as displayed by most mail programs.

Look at the example at https://en.wikipedia.org/wiki/Simple_Mail_Transfer_Protocol  and notice both the protocol "RCPT TO:" and "MAIL FROM:" that most mail checkers validate against for blantant fraud.  Then go down a bit and look at the message body, the stuff after the "DATA" protocol command.  The stuff there is what most mail programs display and its just data, you could put anything you like in there, including "techsupport@bitmain.com" or whatever.

I would be curious if someone that received the e-mail would look at the headers (an option turned off in most mail programs but that can be turned on) and see what the sending "MAIL FROM:" was?