So that's a definite no then?
Yes, we're not big Google fan etc ourselves, but no matter how many
blocks / bans you put in place via Apache2 and Nginx, spammers just re-locate and thus, the Contact Us add-on is subject to abuse IF there's no other protocol check applied in the process of a message being submitted.
IF for example the Google reCAPTCHA setup was replaced by a slick @cflsystems add-on
that vetted zen.spamhaus.org barracudacentral.org etc etc for SBL / CSS / XBL / PBL
offenders - then that would surely be a winner would it not?