Can you provide a citation for that? It seems to be like it would be impossible to show proof that such an email was received[1], which I imagine is necessary to declare the subpoena served in a court of law. We do have some other means for sending things like that through the internet (mostly used by lawyers and courts), but I find it hard to believe that merely sending an email without (at the very least) prior contact where the servee indicates subpoenas can be served via email would hold up in court.

[1]: IIRC, in my country the courts ruled that a) SMTP logs of sending an email are not sufficient technical proof of delivery and b) even if it was, that's not enough because you cannot be expected to regularly check your email account and read new mail. Things might be different in the U.S., that's why I'm asking.

I don't know any jurisdiction where email is a valid way of serving a subpoena. There is actually a little bit of debate about it, but most people agree that in the federal system, a subpoena must be hand-delivered.

No evidence of receipt. No witness.