A unique number assigned to a list member, usually by the email-broadcast software, and used to track member behavior (clicks, subscribes, unsubscribe) or to identify the member to track email delivery.
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.