There is no limit to the number of referrals you may make when you send links to your friends via email. We do limit the number of times your referral links are active during a 12-month period. Once any combination of your links are clicked 12 times during this 12-month period, any other links you’ve sent will no longer be valid. A new 12-month period will begin 366 days after your first referral link is clicked.