validate a textbox-error provider

Question

Hi! i want to validate a textbox, where the email is introduces. First i check if the email is too short, and it works, then i try to check if it ends with @yahoo.com or @gmail.com but it doesn't work fine. I guess it's a problem with Substring. Any help? thks.

 private void emailTxt_Validating(object sender, CancelEventArgs e)

        {

            string mesaj = null;

            string email = emailTxt.Text;

            int lungime = email.Length;

            if (lungime < 11)

            {

                mesaj = "E-mail prea scurt!";

                this.errorProvider1.SetError(this.emailTxt, mesaj);

            }

            else

            {

                string text = email.Substring(lungime - 12, 10);

                if (text != "@yahoo.com" || text != "@gmail.com")

                {

                    mesaj = "E-mail: [email protected] sau [email protected]!";

                    this.errorProvider1.SetError(this.emailTxt, mesaj);

                }

            }

        }