question about sending email

[Crespo]

hi,every one! I have a question about sending emails.My codes works well
over some smtp servers,but doesn't over the others. My codes is listed
belowed:
try
{
MailMessage mailObj = new MailMessage();
mailObj.To.Add(receipientAddr);
mailObj.From = new MailAddress(senderAddr);

mailObj.Subject = "very good";
mailObj.Body = "thank you";

mailObj.IsBodyHtml = true;
mailObj.Priority = MailPriority.High;
mailObj.BodyEncoding = System.Text.Encoding.UTF8;


System.Net.Mail.SmtpClient client = new
System.Net.Mail.SmtpClient(smtpServerIP);
client.UseDefaultCredentials = false;
mailObj.SubjectEncoding = System.Text.Encoding.UTF8;
client.Credentials = new
System.Net.NetworkCredential(this.tb_mailUserName.Text,
this.tb_mailUserPassword.Text);
client.DeliveryMethod = SmtpDeliveryMethod.Network;
client.Send(mailObj);

}
catch(Exception ex)
{
MessageBox.Show(ex.Message.ToString());
return;
}

when smtpServerIP is specified with some smtp server ips, the mail can be
delievered correctly.But over some smtp servers such as "smtp.21cn.com",the
codes didn't throw any exception and seemed to have work well,but when I
logined mail.21cn.com,I could not find the expectedly incoming mail. Could
anyone help me?

Crespo
2006-07-03

 

[Greg Young]

It could be that the mail is getting caught by a filter somewhere.

A perfect example of this would be that some servers do a reverse lookup. If
the IP address you are sending from does not matchup one of the MX records
defined for the domain you are sending from they will not deliver it.

One thing that may help would be to save the conversation ...
http://www.systemnetmail.com/faq/4.10.aspx includes info on how to log the
conversation.


Cheers,

Greg Young
MVP - C#
http://codebetter.com/blogs/gregyoung

 

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

Many ISPs have closed the port used by SMTP, so that you can only send
mail using their mail server, to prevent spamming.

 

[Crespo]

Thank you,Mr Andersson. I don't understand well what you explained,could you
give me more detail? Thank you very much.

Crespo

 

[Crespo]

thank Gred Young very much. But I don't understand well,could you give more
detail.Thanks very much.

Crespo

 

[=?ISO-8859-1?Q?G=F6ran_Andersson?=]

What specifically was it that you didn't understand?

 

[Crespo]

Thank you,i have got it.Your explaination is good. Thanks again.

Crespo.

 

[Greg Young]

What part are you not understanding? Can you get the conversation between
your client and the SMTP server (directions in link).

Cheers,

Greg