How do I limit RSVPs to one per email address?
From the Form tab on your page's editing toolbar, check off the Limit one RSVP response per email to make sure that each guest can only RSVP once.
This allows only one RSVP response per email address.
If space is very limited, we recommend sorting your RSVPs by First Name and Last Name and checking to ensure guests didn't use multiple email addresses to RSVP. The hotter the event, the more desperate they may be to attend!