Postfix has the feature you require[0]. Does google support anything along these lines? https://serverfault.com/questions/321109/how-to-prevent-remote-hosts-fr

Postfix has the feature you require[0]. Does google support anything along these lines? https://serverfault.com/questions/321109/how-to-prevent-remote-hosts-from-delivering-mail-to-postfix-with-spoofed-from-he https://serverfault.com/questions/321109/how-to-prevent-remo...