Opt-in MLM leads are one of the best ways to attract new customers or sign up new members in your multi-level marketing plan. What are opt-in leads, you ask? That is a lead that had to fill out a questionnaire over the Internet and respond to an e-mail so that the lead generating company could email them for confirmation. Double opt-in mlm leads are the best since they have expressed interest in your type of company twice before you ever contact them. It’s like having a fish with its mouth wide-open, waiting for the hook.