A: The status "unknown" means we couldn't find out the condition of that email. In our verification process, most of the time this happens when the server of the email address you are verifying do not respond on our request (although the external look of their server configuration seems good, there can be internal configuration issues). The result can be unknown if their email server is too slow or too busy at that moment. It is also possible that their firewall configuration is set in a way that does not allow us to check the status. A lot of the time if you verify the unknown emails after some time, you will find additional verified emails (as their server may respond at that time). If you are sending emails to a scraped or purchased list, it is better to avoid them. But if you trust the email list (your own subscribers) and the ration of unknow emails is low, you can send emails to them (keep in mind that you can get some bounces from them as we are not able to verify them). Let us know if you have any other questions.