unable to send email

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SharePoint

In my application, I need to upload a document and after it is uploaded, a mail haas to be send to a particular id. for this i did the coding. there is no error and the document is uploded but sending mail portion is not working. the mail sending portion is like this

MailMessage message = new MailMessage();
                        message.From = new MailAddress("from");
                        message.To.Add("to");
                        message.Subject = "Test mail";
                        message.Body = " This is a test ";
                        message.IsBodyHtml = true;
                        string smtpUrl = web.Site.WebApplication.OutboundMailServiceInstance.Server.Address;
                        SmtpClient smtp = new SmtpClient(smtpUrl);
                        smtp.Send(message);

Pls help me if you know the reason.

Thanks