Ah, didn't see the 'email' word in the original.Well, no. He got an email from some unknown guy which alleges some claim and alleges some lawyer costs. That isn't quite the same thing.
The legal process is rather long. He got a C&D order, which is right near the very beginning of the process.
If you get a C&D order, you get it via certified mail (that is, on paper), and you get an invoice for the attorney's fees with the letter along with a threat of legal proceedings if you do not comply within 14 days (or a similar time period).
As noted in my earlier reply with "signature and proof of delivery", I totally agree. Legal demands are sent through paper channels that require real signatures to ensure delivery. Email doesn't cut it. Yeah, that kind of email bill is safe to ignore. A real C&D demand, however, is not.