MailVerify   
by NehuenMultimedia - Marcelo Fassardi   

MailVerify is the fastest selling email validation software on the internet! It's also the easiest to learn and use!
Mailverify does it all for you:
An accurate syntax check
A domain check by looking up MX records
A username test using SMTP,EXPN and VRFY
We've packed a full set of solid, professional networking code into the application
MailVerify works by performing a special type of DNS lookup . This lookup ensures that the domain of the email address is fully qualified to receive email. Although it is impossible for validation to be 100% foolproof, MailVerify can reduce the bad email addresses in your database by up to 70% or more! improvings the quality of your email addresses by filtering out more bad addresses than any email validation tool.