We decided not to go by PM, its difficult, confusing to manage and not public.
We will restrict all address entries in our website by IP and we will use recaptcha to prevent abuse.
All participant addresses will be visible in the website.
IP is as easy to change as email.
Yes, the best would be different IPs and also a member of this forum with at least jr member rank.
That's a lot more work for cheaters but of course it can be done, no doubt.
Still you are less likely to see 50 addresses from the same person and the list of 1000 getting filled up within 30 minutes or so.