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

protected void Button_Click(object sender, EventArgs e) 
{
string username = string.Empty;
            string password = string.Empty;
            string constr = ConfigurationManager.ConnectionStrings["GlobalConnection"].ConnectionString;
            using (SqlConnection con = new SqlConnection(constr))
            {
                using (SqlCommand cmd = new SqlCommand("SELECT UserName,Password FROM Login_Mst WHERE EmailID = @EmailID"))
                {
                    cmd.Parameters.AddWithValue("@EmailID", txtemail.Text.Trim());
                    cmd.Connection = con;
                    con.Open();
                    using (SqlDataReader sdr = cmd.ExecuteReader())
                    {
                        if (sdr.Read())
                        {
                            username = sdr["UserName"].ToString();
                            password = sdr["Password"].ToString();
                        }
                    }
                    con.Close();
                }
            }
            if (!string.IsNullOrEmpty(password))
            {
                MailMessage mm = new MailMessage("ramdasshinde092@gmail.com", txtemail.Text.Trim());
                mm.Subject = "Password Recovery";
                mm.Body = string.Format("Hi {0},<br><br>Your password is {1}.<br><br>Thank You.", username, password);
                mm.IsBodyHtml = true;
                SmtpClient smtp = new SmtpClient();
                smtp.Host = "smtp.gmail.com";
                smtp.EnableSsl = true;
                NetworkCredential NetworkCred = new NetworkCredential();
                NetworkCred.UserName = "email@gmail.com";
                NetworkCred.Password = "password";
                smtp.UseDefaultCredentials = true;
                smtp.Credentials = NetworkCred;
                smtp.Port = 587;
                smtp.Send(mm);
                Label2.ForeColor = Color.Green;
                Label2.Text = "Password has been sent to your email address.";
            }
            else
            {
                Label2.ForeColor = Color.Red;
                Label2.Text = "This email address does not match our records.";
            }
        }