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Note the Contact link in the footer: you can email the mods directly. In my experience they're very responsive.

hn@ycombinator.com ???

and how do they verify that the email requesting an account be deleted, is coming from the actual owner of that account?

Rather than ask random people on the forum, I suggest emailing the mods and asking them directly. They're clearly authoritative in this regard.

If it’s from the email you signed up with, that’d be a good sign.