ASP.NET

  public static void CreateTestMessage1(string server, int port)
  {
      string to = "someone@somewhere.com";
      string from = "me@somewhere.com";
      string subject = "Using the new SMTP client.";
      string body = @"Using this new feature, you can send an e-mail message from an application very easily.";
      MailMessage message = new MailMessage(from, to, subject, body);
      SmtpClient client = new SmtpClient("smtp server name");

      client.Credentials = new System.Net.NetworkCredential("username", "password");

try {
        client.Send(message);
}
      catch (Exception ex) {
        Console.WriteLine("Exception caught in CreateTestMessage1(): {0}",
              ex.ToString() );
}
  }

string AddAtt = "C:/MyFile.txt";//File or image or whatever path
MailMessage message = new System.Net.Mail.MailMessage();
message.Body = strBody;//Message body
message.Subject = strSubject;//Message Subject
message.From = new MailAddress(strFrom, Txt_NameOf.Text);//Mail and mail's name from
message.To.Add(new MailAddress(strTo, Txt_NameTo.Text));//Mail and mail's name to
message.Attachments.Add(new System.Net.Mail.Attachment(AddAtt));//<<HERE attachment