kamili on "[Plugin: Contact Form 7] wpcf7_before_send_mail - Trigger or Add Error Message"

Thanks so much. I got it solved by using your filter email and text filters (e.g. add_filter('wpcf7_validate_email*','wpcf7_validate_gfemail', 10, 2);, WordPress' email_exists() function, and Michael Simpson's cfdb custom validation concept: http://cfdbplugin.com/?page_id=904

Cheers!