// send smtp from from c#/.net

System.Web.Mail.MailMessage message=new System.Web.Mail.MailMessage();

message.Fields.Add( "http://schemas.microsoft.com/cdo/configuration/smtpauthenticate",1 );
message.Fields.Add( "http://schemas.microsoft.com/cdo/configuration/sendusername","SmtpHostUserName" );
message.Fields.Add( "http://schemas.microsoft.com/cdo/configuration/sendpassword","SmtpHostPassword" );

message.From="from e-mail";
message.To="to e-mail";
message.Subject="Message Subject";
message.Body="Message Body";

System.Web.Mail.SmtpMail.SmtpServer="SMTP Server Address";
System.Web.Mail.SmtpMail.Send(message);

// Quick Mail class

    static class QuickMail
    {
        public static void SendMail(string from, string to, string subject, string messageText, bool isHtml)
        {
                        SmtpClient mymail = new SmtpClient(ConfigurationManager.AppSettings["localsmtp"]);
                        MailMessage message = new MailMessage(from, to, subject, messageText);
                        message.IsBodyHtml = isHtml;
                        mymail.Send(message);
        }
    }

Occassionaly you have a internal mailserver on a machine which has a hostname like machine.example but for mail purposes your machine is known to the outside world as mail.example.com one can use the following helo_data on in your transports for exim to announce yourself as mail.example.com:

remote_smtp:
  driver = smtp
  helo_data = mail.example.com