From the Model Mayhem FAQ:

I am not finding any emails from Model Mayhem – what do I do?
First, check to see if the email from Model Mayhem is in your spam box.

If it’s not there, try adding to your email as a safe sender.

If this doesn’t help, then it’s possible that your email provider is somehow blocking the emails from Model Mayhem. We recommend contacting them to see if they’re blocking the emails.

If all of this really doesn’t work, we can always help you change your email to something else so you can get your account verified!

If you are having issues validating your account, click to resend the verification email.