No need to explain yourself... they were just suggestions.
As for bots, I figure that most do bypass the form altogether, but I thought a measure like disallowing banned emails from being entered could at least prevent some bots from ever submitting the form, and maybe even stop some manual spammers in their tracks (the ones who normally get through CAPTCHA).. but I realize that if they're determined they'll just keep entering emails until they find one that's not banned.