PHP Mail tester
A PHP script to check if an email address exists, very useful in detecting email identity forgeries, spam bots or automatic mail responders
If the domain exists, it then asks the mail server if that email username exists as well.
The entire 'PHP Mail tester' script is contained in one single PHP file and can be hosted on any Web server with ease.
Use it wisely since many MX servers tend to block too many MX records inquiries coming from the same IP address.