EDIT: “nearly any email rainbow table”, i.e. 1-10 characters cross joined with all domains for a given tld. You’re correct that brute force with an entropy of

EDIT: “nearly any email rainbow table”, i.e. 1-10 characters cross joined with all domains for a given tld. You’re correct that brute force with an entropy of 3 per bit would still be too big for rainbow table usage (like 10^15 PB too big).