用ASP写的邮件发送，在自己电脑的iis上部署可以发送，但是部署到服务器上不能发送了

private static String sendingMail(Object textContent, Object emailAddress)
{

            String message = "邮件发送成功";

            //string smtpService = "smtp.sheny.com.cn";

            //string sendEmail = ".com.cn";
            //string sendpwd = "";

            string smtpService = "smtp.mxhichina.com";

            string sendEmail = "";
            //string sendpwd = "ouaqlwlubykxbdbe";
            string sendpwd = "";
            //确定smtp服务器地址 实例化一个Smtp客户端
            SmtpClient smtpclient = new SmtpClient();
            smtpclient.Host = smtpService;


            //确定发件地址与收件地址
            MailAddress sendAddress = new MailAddress(sendEmail);
            //MailAddress receiveAddress = new MailAddress("@qq.com");
            MailAddress receiveAddress = new MailAddress(emailAddress.ToString());
            //构造一个Email的Message对象 内容信息
            MailMessage mailMessage = new MailMessage(sendAddress, receiveAddress);
            mailMessage.Subject = "订舱信息" + DateTime.Now;
            mailMessage.SubjectEncoding = System.Text.Encoding.UTF8;
            //mailMessage.Body = "测试邮件发送成功！！！";
            mailMessage.Body = textContent.ToString();
            mailMessage.BodyEncoding = System.Text.Encoding.UTF8;

            //邮件发送方式  通过网络发送到smtp服j
            smtpclient.DeliveryMethod = SmtpDeliveryMethod.Network;

            //如果服务器支持安全连接，则将安全连接设为true
            smtpclient.EnableSsl = true;
            try
           {
            //是否使用默认凭据，若为false，则使用自定义的证书，就是下面的networkCredential实例对象
            smtpclient.UseDefaultCredentials = false;

            //指定邮箱账号和密码,需要注意的是，这个密码是你在QQ邮箱设置里开启服务的时候给你的那个授权码
            NetworkCredential networkCredential = new NetworkCredential(sendEmail, sendpwd);
            smtpclient.Credentials = networkCredential;
            ServicePointManager.ServerCertificateValidationCallback =
            delegate (Object obj, X509Certificate certificate, X509Chain chain, SslPolicyErrors errors) { return true; };
            //发送邮件
            smtpclient.Send(mailMessage);


        }
    catch (System.Net.Mail.SmtpException ex) { message = ex.Message; }
    return message;
}

网络的问题，主要是防火墙还有网络连接是否通，还有你的服务器是否被对方SMTP服务器拉黑了。一些小机房的服务器，因为你的“邻居”总是在乱发垃圾邮件，所以邮件服务器提供商可能封掉了这个网段全部的ip，那么你只能换一个机房了。