Asp.net Registration Form, need email validation in C#

Question

using System;

using System.Collections.Generic;

using System.Linq;

using System.Web;

using System.Web.UI;

using System.Web.UI.WebControls;

using System.Data;

using System.Data.SqlClient;

public partial class _Default : System.Web.UI.Page 

{

    

    protected void Page_Load(object sender, EventArgs e)

    {

        

    }

    protected void DropDownList5_SelectedIndexChanged(object sender, EventArgs e)

    {

    }

    protected void Clear_Click(object sender, EventArgs e)

    {

        TextBox1.Text = "";

        TextBox2.Text = "";

        TextBox3.Text = "";

        TextBox4.Text = "";

        TextBox5.Text = "";

        TextBox6.Text = "";

        TextBox7.Text = "";

        TextBox8.Text = "";

        TextBox9.Text = "";

        TextBox10.Text = "";

        TextBox11.Text = "";

        RadioButtonList1.SelectedValue = null;

        TextBox12.Text = "";

        DropDownList4.SelectedValue = null;

        DropDownList5.SelectedValue = null;

        CheckBox1.Checked = false;

        Label21.Text = "";

    }

    protected void CheckBox1_CheckedChanged(object sender, EventArgs e)

    {

    }

    protected void RadioButton1_CheckedChanged(object sender, EventArgs e)

    {

        

    }

    protected void Button1_Click(object sender, EventArgs e)

    {

        SqlDataReader dr;

        SqlConnection con = new SqlConnection("Data Source=SARANYA-TS02\\SQLEXPRESS;Initial Catalog=ss;Integrated Security=True");

        SqlCommand cmd = new SqlCommand("insert into RegistrationForm values('" + TextBox1.Text + "','" + TextBox2.Text + "','" + TextBox3.Text + "','" + TextBox4.Text

            + "','" + TextBox5.Text + "','" + TextBox6.Text + "','" + TextBox7.Text + "','" + TextBox8.Text + "','" + RadioButtonList1.SelectedValue

            + "','" + TextBox12.Text + "','" + TextBox9.Text + "','" + TextBox10.Text

            + "','" + TextBox11.Text + "','" + DropDownList4.SelectedValue + "','" + DropDownList5.SelectedValue + "')", con);

        con.Open();

        cmd.ExecuteNonQuery();

        SqlCommand cc = new SqlCommand("select from RegistrionForm where e-mail Address");

        cc.ExecuteNonQuery();

    }

    protected void RadioButton2_CheckedChanged(object sender, EventArgs e)

    {

        

    }

    protected void TextBox7_TextChanged(object sender, EventArgs e)

    {

        

    }

    protected void TextBox2_TextChanged(object sender, EventArgs e)

    {

    }

    protected void TextBox3_TextChanged(object sender, EventArgs e)

    {

    }

    protected void TextBox9_TextChanged(object sender, EventArgs e)

    {

    }

}

 this is my code i want to modify n email id... after i click submit button if that email id is already exists means i ve to throw exception.... plz help me