Send email in ASP.NET C#

Question

I'm creating a contact page for visitors of my web site to send me email (in C#). When trying, I got an error about EHLO argument(s). Here is my code:

I got the error:

The server response was: Syntactically invalid EHLO argument(s).

Please, help

try
    {
        MailMessage _email = new MailMessage();
        String MessageString = "";
        MessageString = "<br>";
        MessageString += "<b>Message from " + champNom.Value + "</b><br /><br />";
        MessageString += "<br/><br/>";
        MessageString += champMail.Text;
        _email.Subject = "Mail from " + champNom.Value + " (Email adress: " + champEmail.Text + ")";
        _email.From = new System.Net.Mail.MailAddress(System.Configuration.ConfigurationManager.AppSettings["SenderForEmail"].ToString(), "MyName");
        _email.To.Add(new System.Net.Mail.MailAddress(System.Configuration.ConfigurationManager.AppSettings["AdminForEmail"].ToString(), "MyName"));
        if (chkCCMyself.Checked) {
           _email.CC.Add(new System.Net.Mail.MailAddress(champEmail.Text, champNom.Value));
        }
        _email.Body = MessageString;
        _email.IsBodyHtml = true;
        System.Net.Mail.SmtpClient smtp = new System.Net.Mail.SmtpClient();
        smtp.EnableSsl = false;
        //smtp.UseDefaultCredentials = true;
        //smtp.DeliveryMethod = SmtpDeliveryMethod.Network;
        smtp.Host = System.Configuration.ConfigurationManager.AppSettings["HostForEmail"].ToString();
        smtp.Port = 587;
        smtp.Credentials = new System.Net.NetworkCredential(System.Configuration.ConfigurationManager.AppSettings["SenderForEmail"].ToString(), System.Configuration.ConfigurationManager.AppSettings["SenderPswdForEmail"].ToString());
        smtp.Send(_email);
        Page.RegisterStartupScript("UserMsg", "<script>alert('Mail envoyé avec succès...');if(alert){ window.location='contact.aspx';}</script>");
    }catch(Exception err){
        champMail.Text += Environment.NewLine + err.Message;
    }

Thanks in advance

Answer 1

As documented here http://forums.asp.net/t/1622198.aspx?Syntactically+invalid+EHLO+argument+s+emailing

If you email having problem with rejected EHLO or HELO, caused by syntactically invalid argument(s).

1.Possible the hostname contains underscore(_).

2.This is not standard practice, having _ for your domain

3.for example takizo_mail.takizo.com

4.Most of the mail server rejected hostname with underscore.

5.Possibility is a Windows Admin

Answer 2

确保服务器名称中仅包含拉丁字符，并且不包含下划线等特殊符号。

Answer 3

        MailMessage msg = new MailMessage("from@a.com", "To@y.com");
        msg.Subject = "Intraday";
        msg.Sender = new MailAddress("sender@y.com");
        msg.IsBodyHtml = false; //to preserve line breaks and to avoid the need for <br>s
        msg.Body = "Body";
        SmtpClient client = new SmtpClient("Server");
        client.Send(msg);