class GetIP
{
    public static void Main()
    {
          Console.WriteLine (Host name : {0}, Dns.GetHostName());
    }
}
二十、发送邮件：
using System;
using System.Web;
using System.Web.Mail;

public class TestSendMail
{
    public static void Main()
    {
        try
        {
            // Construct a new mail message
            MailMessage message = new MailMessage();
            message.From = from@domain.com;
            message.To   =  pengyun@cobainsoft.com;
            message.Cc   = ;
            message.Bcc  = ;
            message.Subject = Subject;
            message.Body = Content of message;
           
            //if you want attach file with this mail, add the line below
            message.Attachments.Add(new MailAttachment(c:\\attach.txt, MailEncoding.Base64));
 
            // Send the message
            SmtpMail.Send(message); 
            System.Console.WriteLine(Message has been sent);
        }

        catch(Exception ex)
        {
            System.Console.WriteLine(ex.Message.ToString());
        }

    }
}
二十一、根据IP地址得出机器名称：
using System;
using System.Net;

class ResolveIP
{
     public static void Main()
     {
         IPHostEntry ipEntry = Dns.Resolve(172.29.9.9);
         Console.WriteLine (Host name : {0}, ipEntry.HostName);        
     }
}