An anti-spam program that requires a human being on the sender’s end to respond to an emailed challenge message before their messages can be delivered to recipients. Senders who answer the challenge successfully are added to an authorization list. Bulk emailers can work with challenge-response if they designate an employee to watch the sending address’ mailbox and to reply to each challenge by hand.

Building a Highly-targeted Opt in List: When Money Lies Beneath the Lists
Are you successful with your Internet business? Better yet, do you think you are successful with your online business? When most online entrepreneurs are asked with these questions, they often brush it off.

