Email verification is no secret. All it requires is a little knowledge of the SMTP protocol and your programming language of choice. To prove just how easy it is, I'm going to walk you through the basics using a simple python script. I'm providing this information as-is and completely for free.
Why am I offering this for free?
You may have noticed that I work for Email Hippo, a company whose main product is email verification. At Email Hippo, we are very open about the email verification process; as I said, it is no secret. What separates Email Hippo from a free service or this script, or in fact many of our competitors, is that we can do this with accuracy and in scale (hence the big old hippo).