An email validation service costs less than an email verification service. The reason is the algorithm does mostly matching and removing emails against large suppressions lists. This costs bandwidth and time. Many validation companies also check the mx records which doesn’t harm the IP or domain when requested. When a company offers free email validation, they probably will keep your list and resell it but the cost on their end is minute compared to verification. And here’s why:
Free is never free. When a company offers to scrub your list for free, it’s obvious they do not value their own property. What value can you place on doing something and get nothing in return? That does not work in the business world. Even a good validation company with excellent suppression lists has worth and value. Verification has to have some intelligence behind it. It costs more to manufacturer intelligence in an algorithm.
SMTP handshakes, social network comparing, appending to emails that were delivered to recently, all for the sake of verification, can cost a lot of money in domains, IPs, bandwidth and resources. To simply offer this kind of service free versus validation which is cheaper is ridiculous. The odds and chances are high that when you upload your list, it is unsecured and everything you worked hard for will be traded or sold.
Another warning is look at the website itself. Does it look like the free verification service website is secure? Does it have https? Does it look like they spent a fortune on it? Is there any contact information? Phone number? Address? Do they expose their names? Do they have a valid whois?
So beware of free email verification. Simply put, there is no such thing. You could not even make enough money on google ads to justify the cost of verification so all evidence points to fraud. Remember, your database is your baby. Your livelihood. Paying to have it scrubbed is a better investment than having it done for free. Again, free is never free.