Email Validation is a 40 year old technology. The process of one email server communicating with another email server to see if it will accept an email address was once the very best way to validate an email before you sent it. Today, however that process is not as binary as it once was.
Standard SMTP negotiation has never been able to provide a validation status on Catch All emails or email servers using Grey listing techniques. Using standard SMTP negotiation alone will not provide a validation status for CATCH All email addresses.
RampedUp has created an Email Exhaust Exchange where our customers share email deliverability data on our email addresses. The delivery data allows us to validate Catch All and Unknown email addresses.
For the Catch All email addresses that we cannot validate through deliverability, we take the additional step of querying the server to verify if the email address is valid. We call this step Email Authentication because the response is telling us if the email address is associated with an account hosted by that server.
This isn't SMTP negotiation - its Email Authentication!