If the email is DKIM signed, it's expected that the sender was authorized to send the message.

Any wide spread certificate program will just have the email address as the identity, and it will be authorized by establishing control of the email (just like the majority of certificates used for https are domain control only, no organizational verification, not that organizational verification means much anyway). Anyway, identity is hard; there are many people with my name, including a Pulitzer winning author.