How to send forgot password via e-mial in C# asp,net

protected void LinkButton1_Click(object sender, EventArgs e)
    {
        
        Random rnd = new Random();
        int ram = rnd.Next(1111, 9999);

         SqlConnection con = new SqlConnection("Data Source=(local);Integrated Security=true;Initial Catalog=ProPOSDB");

        // Gmail Address from where you send the mail
        var fromAddress = "checkingforasp@gmail.com";
        // any address where the email will be sending
        con.Open();
        SqlDataAdapter ad = new SqlDataAdapter("SELECT UserName,Password FROM UserInfo Where Email ='" + TextBox1.Text + "'", con);

        DataTable dt = new DataTable();
        ad.Fill(dt);
        con.Close();


        var toAddress = dt.Rows[0][0].ToString();
        //Password of your gmail address
        //const string fromPassword = "yahoo123.com";
        // Passing the values and make a email formate to display
        string subject = "Password";
        string body = ram.ToString();

        SmtpClient client = new SmtpClient();
        client.Port = 587;
        client.Host = "smtp.gmail.com";
        System.Net.NetworkCredential nc = new System.Net.NetworkCredential("noman.szic@gmail.com", "pass");
        client.EnableSsl = true;
        client.UseDefaultCredentials = false;
        client.Credentials = nc;

        // Passing values to smtp object

        client.Send(fromAddress, toAddress, subject, body);



        con.Open();
        SqlDataAdapter ad1 = new SqlDataAdapter("update UserInfo set Password = '" + ram + "' where UserName = '" + TextBox1.Text + "'", con);

        DataTable dt1 = new DataTable();
        ad1.Fill(dt1);
        con.Close();
    }

Server Error in '/ForgotPass' Application.
The specified string is not in the form required for an e-mail address.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.FormatException: The specified string is not in the form required for an e-mail address.

Source Error:
Line 52:         // Passing values to smtp object
Line 53: 
Line 54:         client.Send(fromAddress, toAddress, subject, body);
Line 55: