ConfigurationManager.AppSettings["SMTP"]; null exception

i took this code to send an email. But i dont understand what that configurationManager does, and why it gives me the exception. Here is the full code:

        MailMessage mail = new MailMessage();

    mail.To.Add("makovetskiyd@yahoo.开发者_如何学运维co.uk");

    mail.From = new MailAddress("makovetskiyd@yahoo.co.uk");

    mail.Subject = "Test Email";

    string Body = "Welcome to CodeDigest.Com!!";

    mail.Body = Body;

    SmtpClient smtp = new SmtpClient();

    smtp.Host = ConfigurationManager.AppSettings["SMTP"];

    smtp.Send(mail);

i also changed the last lines to this: smtp.DeliveryMethod = SmtpDeliveryMethod.PickupDirectoryFromIis;

        smtp.Send(mail);

but it would still show a mistake, saying it didnt find IIS server..or something like that

---

You should not use AppSettings an the ConfigurationManager for SMTP configuration. The preferred way is to configure SMTP through the <mailSettings> section in web.config. For example, the configuration for a small website could look like this:

<system.net>
  <mailSettings>
     <smtp from="info@example.com">
        <network host="localhost" port="25" defaultCredentials="false">
     </smtp>
  </mailSettings>
</system.net>

This will allow you to new up an SmtpClient and just send the message without further configuration.

---

ConfigurationManager provides access to configuration files for client applications.

I guess the reason of the error is that the config file of your application does not have a SMTP key in the application settings section.

<appSettings>
    <add key="SMTP" value="..." />
</appSettings>

---

The reason is that there is no such SMTP configuration in the config file. I think you'd better check your web.config. And to make your application stronger, you need to add a default host in case of the config file is incorrect.

string defaultHost = "www.foo.com";
smtp.Host = ConfigurationManager.AppSettings["SMTP"] ?? defaultHost;