An authentication method that requires a human to respond to an email challenge message before the original email that triggered the challenge is delivered to the recipient. This method is sometimes used to cut down on spam since it requires an action by a human sender.
Building an Opt-In List, Building Relationships
If you aim for success, you must do everything within your means to achieve that. You just donÃt go on sitting there in your house complaining about not getting as much profit as you expect.
