@dansup @pixelfed as you are allowing plus-addressing in the email, maybe a "there are X other accounts with the same plus prefix" and "there are X other accounts on the same mail domain, of which Y are disabled, Z are blocked, N have spam reported" as a good indicator (maybe a "domain trust score?)

And as a bonus note that gmail is super special; the local part (left hand of @) one can insert dots anywhere: eg d.a.niel.super.nault@ is the same address.. fun for antispam scoring...