Hi,
If you want to check email is exists or not .
there are so many ways for it.
Easy and no-cost method is solution1
but it is some what late and waiting process.
If you want to some webservices for this there are plenty of services in market
Here I'm providing one of web service providers for email verification
http://strikeiron.com/Products/EmailVerification.aspx
Based on requirement you've to choose among ways.
All the Best