I tried to join this site nearly 30 times, using different machines, email providers, usernames etc. Whatever combination I could to receive the verification email. (Facebook reject your registration form completely.)
In the end I was only able to join by using my work email. gmail, mail.com, outlook.com etc don't work at all. The verification email isn't in spam, it just never arrives.
It's a serious problem and I think you are losing alot of business due to users who can't join, especially from gmail.