Email Validation in C# Window Application

private void TextBox1_Validating(object sender, CancelEventArgs e)
{
    System.Text.RegularExpressions.Regex rEmail = new System.Text.RegularExpressions.Regex(@ "^[a-zA-Z][\w\.-]*[a-zA-Z0-9]@[a-zA-Z0-9][\w\.-]*[a-zA-Z0-9]\.[a-zA-Z][a-zA-Z\.]*[a-zA-Z]$");
    if (txtEmail.Text.Length > 0)
    {
        if (!rEmail.IsMatch(txtEmail.Text))
        {
            MessageBox.Show("Please provide valid email address", "Error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            txtEmail.SelectAll();
        }
    }
}