You must be thinking of something like this: http://www.webdigi.co.uk/blog/2009/how-to-check-if-an-email-address-exists-without-sending-an-email/ http://www.web

You must be thinking of something like this: http://www.webdigi.co.uk/blog/2009/how-to-check-if-an-email-address-exists-without-sending-an-email/ http://www.webdigi.co.uk/blog/2009/how-to-check-if-an-email-... Merely looking up MX records is something you do for a _domain_ and it's no different than the DNS requests your computer makes when you go to a website.