I have set smtpd_recipient_limit=3, smtpd_recipient_overshoot_limit=3, but it just blocks sending mail to more than 3 accounts from my server to local address, but what I want is to block mails from yahoo or gmail in thsi way, as they send mail to more than 500 users and we will get in trouble. Please let me know what should I do for blocking incoming mails.