Please Help !!!!

My name is CJ and I'm a new member. I was wondering how you invite people to join PictureSocial if you don't have an e-mail address that ends in yahoo.com or gmail.com or one of the other ONLY choices that are offered? I have a ymail.com with is essentially yahoo mail but it's not one of the choices. I would love to invite other photographer friends to join but am stuck at that point. Please help