The remote name could not be resolved: 'smtp.gmail.com'

Source File: e:\Vijaya\Online_Book_Shopping\ForgetPassword.aspx.cs Line: 62

}

protected void Button1_Click(object sender, EventArgs e)
{
    string username = "";
    string password = "";
    string constr = ConfigurationManager.ConnectionStrings["CS"].ConnectionString;
    SqlConnection con = new SqlConnection(constr);
    {

        SqlCommand cmd = new SqlCommand("select Name, Password from dbo.RegisteredUsers where Email=@email", con);
        cmd.Parameters.AddWithValue("Email", txtemail.Text);
        con.Open();
        using (SqlDataReader dr = cmd.ExecuteReader())
        {
            if (dr.Read())
            {
                username = dr["Name"].ToString();
                password = dr["Password"].ToString();

            }

        }
        con.Close();

        if (!string.IsNullOrEmpty(username))
        {
            MailMessage msg = new MailMessage();
            msg.From = new MailAddress("nilusilu3@gmail.com");
            msg.To.Add(txtemail.Text);
            msg.Subject = " Recover your Password";
            msg.Body = ("Your Username is:" + username + "<br/><br/>" + "Your Password is:" + password);
            msg.IsBodyHtml = true;

            SmtpClient smt = new SmtpClient();
            smt.Host = "smtp.gmail.com";
            System.Net.NetworkCredential ntwd = new NetworkCredential();
            ntwd.UserName = "nilusilu3@gmail.com"; //Your Email ID<br />
            ntwd.Password = ""; // Your Password<br />
            smt.UseDefaultCredentials = true;
            smt.Credentials = ntwd;
            smt.Port = 587;
            smt.EnableSsl= true;
            smt.Send(msg);
            lblmsg.Text = "Username and Password Sent Successfully";
            lblmsg.ForeColor = System.Drawing.Color.ForestGreen;
        }
    }

}

        public DataSet Get()
        {
            DataSet dsAllListsOfForm = new DataSet();
            dsAllListsOfForm.Tables.Clear();

            dynamic objCollection; DataTable table;
            using (AppDevSecEntities ctx = new AppDevSecEntities())
            {
                objCollection = (from c in ctx.Departments orderby c.DepartmentName select c).AsQueryable();
                table = Common.ConvertToDataTable<Department>(objCollection);
                dsAllListsOfForm.Tables.Add(table);

                objCollection = (from c in ctx.FunctionalCatagories orderby c.FunctionalCatagoryName select c).AsQueryable();
                table = Common.ConvertToDataTable<FunctionalCatagory>(objCollection);
                dsAllListsOfForm.Tables.Add(table);

                objCollection = (from c in ctx.BusinessUnits orderby c.BusinessUnitName select c).AsQueryable();
                table = Common.ConvertToDataTable<BusinessUnit>(objCollection);
                dsAllListsOfForm.Tables.Add(table);

                objCollection = (from c in ctx.Locations orderby c.LocationName select c).AsQueryable();
                table = Common.ConvertToDataTable<Location>(objCollection);
                dsAllListsOfForm.Tables.Add(table);
            }

            return dsAllListsOfForm;
       }

<asp:Content ID="Content1" ContentPlaceHolderID="MainContent" Runat="Server">
    <section ID="normalElement" runat="server"></section>    
    <section ID="adminPanel" runat="server"></section>
    <section ID="myC" runat="server"></section>    
</asp:Content>

GridView view = new GridView();
DataTable tbl = new DataTable();
DataColumn idCol = tbl.Columns.Add("COL_A");
idCol.DataType = System.Type.GetType("System.String");
DataColumn nameCol = tbl.Columns.Add("COL_B");
nameCol.DataType = System.Type.GetType("System.String");
DataColumn descrCol = tbl.Columns.Add("COL_C");
descrCol.DataType = System.Type.GetType("System.String");
DataColumn delCol = tbl.Columns.Add("COL_D");
delCol.DataType = System.Type.GetType("System.Boolean");
view.DataSource = tbl;
view.DataBind();
myC.Controls.Add(view);