In order for guests that signed up with Facebook to receive marketing emails, they'll need to have given permission to access and share their email. If they do not, then on account generation, Facebook sends an email like email@example.com instead of the guest's email. If they later authorize the sharing of their email, that email will be sent to Punchh and it will fill out the secondary email field. With that email, guests will now be able to receive marketing emails.
If further assistance is required, submit a ticket to Punchh Support. (For help submitting a ticket, click here)