Sacha Greif's DIY email referral system, which utilized Zapier, resulted in 4X normal email newsletter signups when 2.3% of his list decided to refer someone else. A double-sided referral system was used, where both parties get rewarded for some action. The system required an email newsletter signup form, a transactional email service provider like Mandrill or Mailgun, and an account at Zapier. To set up the system, one needs to create a custom link to the referral form, add hidden fields to the form, and use Zapier's Zaps to send emails to both the referrer and the person referred, appending their email addresses to the Wufoo link. The system is designed to incentivize people to sign up to the email newsletter with something desirable, such as credits for a product or an e-book.