Email verification can be achieved through numerous ways. Intelligence, smtp handshakes, appending or all the above. The goal for email verification is to remove bounces (hard or soft), vacation emails, challenge responses, replies from list servers, feedback reports (if needed), mail block relays, forwarders and false positives.
Email Intelligence is information gathering and reporting. It fits along with the appending model below but goes much further. Many companies have access to data that offers a clue to an email’s existence. For example, if a company has a list of all Facebook user email addresses (the ones they use to login to Facebook) then this kind of intelligence can be classified as deliverable or be set as some type of priority. Some verification companies combine many intelligent API platforms together to give an email a rating rather than sending an email itself through an smtp handshake to get the results. Intelligent platforms save time and is faster than smtp.
Smtp handshake verification is the act of physically sending an email with text or blank to achieve a response from the recipient’s admin. This process is tough and is quickly blocked, blacklisted or both which produces many false positives in its path. Collecting data this way is tricky and time consuming but can achieve a level of success if you understand each ISP deliverable threshold per IP and through pmta tricks.
Appending verification is the most common form, but most verification companies will not tell you. Most if not all verification companies send advertisements themselves and keep a track of the deliverables and bounces with date/time stamps. It’s easy to build an appending platform and track emails but the problem is, unless you are sending emails daily to the entire list, you will not have a real up-to-date list of deliverables and bounces. Appending verification works well with small lists but not in the billions.
This is why email verification companies have different pricing. If you combine all 3 above (intelligence, smtp & appending), then the odds of an email being a false positive becomes really rare. In this case, the more you spend for verification, the more accurate the results. Prices for verification can range anywhere from $300 to $10,000 per 1 million records. The more you spend, the more intelligence is/are behind the results.