Most of us are familiar with the terms white listing and black listing. There is also grey listing which typically means that a mail server will drop the first or more smtp connections from an IP address that is connecting for the first time and making the assumption that a properly configured mail server, as opposed to a broken spambot, which try to resend legitimate email again later. Waitlisting is accepting an email and generating an email response back to the original sender forcing them to acknowledge that the email is not spam before the email will be delivered to the intended recipient. What do you think about the concept of waitlisting? I've seen a couple companies that provide this service. I'd think that it would generate a lot of email toward non-existent email accounts and could even be used to joe job someone. What are your experiences with either providing the service or communicating with a contact who uses this type of service?