private void MtxtEmail_Validating(object sender, CancelEventArgs e)
 {
     if (!RegularExpression.EmailValidation(MtxtEmail.Text.ToString()))
     {
         var message = MessageBox.Show("Please enter a valid Email Address", "Error", MessageBoxButtons.RetryCancel,
                                       MessageBoxIcon.Error);
         if (message == DialogResult.Retry)
         {
             MtxtEmail.SelectAll();
             e.Cancel = true;
         }
     }
 }