In some edge cases, professional emails cannot be verified with the Email Verifier tool.
This can be because the domain associated with the email is grey-listing/blocking the email verification process and not allowing Hunter to provide a full report for it.
The Email status for similar emails will be "BLOCKED".
Unresponsive email server
In some occasional cases, Hunter can't verify an email address since the email server associated with it is unresponsive or due to another similar issue on the email server side.
As the verification cannot be performed at all, the following message will appear instead of the verification status: "We failed to verify the email address for reasons outside of our control. We advise you to retry later."
As we cannot verify the email, no credit is used.