[Perz1val]

One by one, but I think the question is about the entire domain name

[Brajeshwar]

You can have haveibeenpwned.com check for the custom domain itself. For instance, I get notified if any email of our family domain get leaked (not just mine).

[wongarsu]

If you sign in that's an option on your dashboard. You need an account because you need to verify the domain is yours