i sending a mail but i am getting problem while sending the mail's plz help me

protected void Btn_Submit_Click(object sender, EventArgs e)
    {
        string style = "<span style="color:Green;font-weight:bold;font-size:14px;">";
        string uid = System.Configuration.ConfigurationSettings.AppSettings["gmailid"].ToString();
        //string mailfromid = System.Configuration.ConfigurationSettings.AppSettings["noreplyid"].ToString();
        string mailfrompwd = System.Configuration.ConfigurationSettings.AppSettings["noreplypwd"].ToString();

        string Body = "You Have Subscribe E-Paper...";
        string Subject = "New Subscription";
       // Email(mailfromid, mailfrompwd, uid, Body, Subject);
        Email(uid, mailfrompwd, uid, Body, Subject);
    }

    public void Email(string from, string frompwd, string to, string body, string subject)
    {
       
        MailMessage mail = new MailMessage();
        mail.From = new MailAddress(from);
        mail.IsBodyHtml = true;
        NetworkCredential mailAuthentication = new NetworkCredential(from, frompwd);
        SmtpClient smtp = new SmtpClient("smtp.gmail.com", 587);
        smtp.EnableSsl = true;
        smtp.UseDefaultCredentials = false;
        smtp.Credentials = mailAuthentication;
        mail.To.Add(new MailAddress(to));
        mail.Subject = subject;
        mail.Body = body;
    }</span>