private void charactersComboBox_SelectionChanged(object sender, System.Windows.Controls.SelectionChangedEventArgs e)
        {
            switch (CharactersComboBox.SelectedIndex)
            {
            case 0: EmailTextBox.SetDefaultAsciiSpecialChars(); break;

            case 1: EmailTextBox.SetExtendedAsciiSpecialChars(); break;

            case 2: EmailTextBox.SetExtendedQuotedAsciiSpecialChars(); break;

            default: throw new NotSupportedException();
            }
        }