Hi :)
How concernt are you about leaking your personal information by using a custom-domain for emails?
Because anyone could see, who registered the domain, correct?
I have seen people with an axe to grind use frivolous lawsuits to reveal domain identities, you don't actually have to do anything wrong for that to happen.
I think the only issue with that is that when/if it is found out then the domain will likely be seized because you violated your contract with the registrar to provide accurate information.
My understanding is that they don't... practically at all. But if compelled by a court to give your information, they could later learn that the information you provided was false. Or maybe someone reported you and they ask for some type of verification. Either way, it's one of many tactics that can be used against someone, even if you only gave fake information to protect your own privacy.
Frivolous DMCAs have also been used to reveal identities of people someone didn't like.