Interesting idea. I have to fork over a bunch of very sensitive information so you can search through data leaks for it? If so, I'd think you would become a big target to be hacked yourself.
Additionally, if you're digging through leaked/hacked/stolen data, you by definition have to possess it. I wonder what the legality of possessing that data is, let alone selling indirect access to it?
Everything listed on the site under "Credential Hero Protects Your Employees' Information" was my initial thought.
Since you've asked I suspect that you are only looking for email addresses and these are simply examples of data that could be associated with a leaked address.
Additionally, if you're digging through leaked/hacked/stolen data, you by definition have to possess it. I wonder what the legality of possessing that data is, let alone selling indirect access to it?