I've tried to use git notes over the years but unfortunately notes are tied to a specific commit hash. It's a blessing and a curse.
Works great for some types of review system, or for "tagging" things related to deploy. Notes on commits on the master/main branch, which doesn't get rebased? Awesome thing, they work.
But you can't as easily use them on branches: the moment a branch whose commits had notes is rebased, and SHAs change, good-bye notes associated with the "previous" SHAs :/
Italy's "PEC"[1] (Posta Elettronica Certificata, or Certified Electronic Mail) comes pretty close.
There's even an RFC[2] for it.
In order to get one, an individual has to prove their identity via a government-issued ID (ID card or passport), and that email address can henceforth be used to send emails for all official correspondence as if it were certified/verified mail, with the added bonus that both parties "know" the identity of the other party (i.e. the company knows it was very likely me who sent it, as they trust that the people in charge of having verified my ID did their job) and with the added bonus of the _contents_ of the email also being certified to have been sent from that recipient to that destination address, and not to have been tampered with (great thing to have for lawsuit reasons), unlike "standard" registered mail, who only certified that a letter has been sent and picked up.
That seems risky.