Not a lot. We can even verify other country email addresses without issues. We are not limited to the just United States. We can verify ANY email address in the world.
Every time our system is unable to determine its validity, we automatically have it registered for our developers to have a look at.
We will get in touch with the customer who uploaded this list and let them know that we weren't able to verify some of the email addresses they have in the list and then our developers will provide them with a verifier list once we have the fix or refund their money for the inconvenience.