No doctor should be writing that email in the first place; it would be an example of such a flagrantly negligent treatment of PHI that cryptographic signatures and reputability are kind of irrelevant.
Email is used outside of countries with these kinds of protections. For example, I know someone who had an STI test in Thailand and the results did indeed come via email.
Even if this example is imperfect, it's really not that hard to imagine a scenario where some type of compromising information is sent to you. Perhaps even accidentally.
Even if this example is imperfect, it's really not that hard to imagine a scenario where some type of compromising information is sent to you. Perhaps even accidentally.