How?
We're a cryptocurrency gambling site. The typical high roller signs up using a throwaway email address and uses TOR or VPN. They deposit, play and withdraw and then never use the account again. Sending people an email asking for information is not something that happens in this industry.
Edit: I forgot to also point out a lot of our older accounts don't even have an email address as it wasn't required for the first few years and accounts were only created by BTC address.
Thanks for explaining - did not think of that.
I'm just trying to think of ways that manual interaction is required.
The company I work for had a similar problem with a monthly competition they held last year to promote their 25th anniversary, they tried everything after the 3rd mth.
Only things (unsure if it was a combination of these or one)
Email verification, 3 question survey/question based on the site, and a Captcha. - entries dropped a good 40% after the third month and was consistent until the final month.