Regarding Email Sending Problem

Question

MailMessage message = new MailMessage();MailAddress from = new MailAddress([email protected], "suresh");

SmtpClient client = new SmtpClient

client.Credentials =

client.UseDefaultCredentials = True;

client.DeliveryMethod =

client.Send(message);

Please send me the solution.

Thanks,

Suresh.

When i sending mail, some of the client doesn't getting mail.
I am getting some Undeliverable Messeges:
1.SmtpDeliveryMethod.PickupDirectoryFromIis;

new NetworkCredential("un","pwd");You do not have permission to send to this recipient. For assistance, contact your system administrator.
2.Could not deliver the message in the time limit specified. Please retry or contact your administrator.
3.The destination server for this recipient could not be found in Domain Name Service (DNS). Please verify the email address and retry. If that fails, contact your administrator.