What is the best self-hosted mail service?

why not setup your domain with proton or tuta.

and I wonder what you mean by keeping it private, you can just use different aliases, I personally use my domain with proton and I have one anyone can email me with and one that is reserved for private matters or local that I don’t mind sharing or needed.

eg.
I have
gorupublic@gorujokun.cy, Public email
and one private that I do not share publicly, same domain though ([redacted]@gorujokun.cy)

also I looked at the sent emails, the pgp signing key is reffering to the email you sent to, so if I sent on my public email, the public key is shown for: gorupublic@gorujokun.cy

private:
image [Look at the last 2 digits at least on the hex that they’re different]
public:
image