Just like Amazon, Netflix or Facebook, a valid email address is required to sign up for an account. Your patients will receive important communication regarding your membership via email (monthly receipts, declined payment notices, etc.).
If you have a patient in your practice who wants to join your membership but they don't have an email address, you might recommend they take a few minutes to sign up for a free account on Gmail, Yahoo, or another provider. We've also been given the feedback that some patients will "borrow" a close family member's email address with the knowledge that the family member will receive the automated communication on their behalf.