Org.BouncyCastle.Pkix.PkixNameConstraintValidator.EmailIsConstrained C# (CSharp) Method

        private bool EmailIsConstrained(String email, String constraint)
        {
            String sub = email.Substring(email.IndexOf('@') + 1);
            // a particular mailbox
            if (constraint.IndexOf('@') != -1)
            {
                if (email.ToUpper().Equals(constraint.ToUpper()))
                {
                    return true;
                }
            }
            // on particular host
            else if (!(constraint[0].Equals('.')))
            {
                if (sub.ToUpper().Equals(constraint.ToUpper()))
                {
                    return true;
                }
            }
            // address in sub domain
            else if (WithinDomain(sub, constraint))
            {
                return true;
            }
            return false;
        }