osCommerce Error : "Your E-Mail Address does not appear to be valid - please make any necessary corrections."

[Guest]

I have a client who has an osCommerce site. When a user tries to register they receive this error even when their email is valid. I entered my own email address with no luck as well. I checked the configuration and "Verify Email Addresses Through DNS" is set to false. What else could the problem be?

 

I know, not very pretty, but it's what they got :

https://www.ip6gold.com/cart/create_account.php

 

Any Ideas?