Check whether Email address exists without Email confirmation in ASP.Net

Gentlemen;

In addition to the process of regex syntax validation of Email Addresses entered by users, I'm trying to check if the entered email address is a real one and does exist?

The best I could achieve is to "Ping" the host the email address is associated with. But there are some other terms in the industry like Handshaking with Email Server, etc.

Any ideas/recommendations? ... not necessarily with 100% confirmation accurary!