So the option is pretty obvious - let’s email myself, to my secondary email, the link. If you have more than an allotted number of requests coming from the same IP address, there is a high-probability that the same client is issuing the request, and therefore invalidating the requests to shift the position in the wait list. When a user submits an email, do not move the original user’s position in the wait list until they confirmed that the shared email is actually owned by a person.