how send bulk mails effectively from asp.net(c#) code using "smtpClient.Send(message);"?

Question

I've set up a windows service to do the bulk mailing functionality which executes it batch by batch.

The service fetches one batch from DB during its schedule and after each batch i've given a delay of 20 seconds.

Do this prevent from considering the mails as spam or as bulk? If so do my code performs what i require. My code is as follows:

//get the batch and execute in a child thread and need to continue only after the  thread get terminated.

 for (int i = 0; i <= QueueCount/20;i++)
 {
      Thread newThread = new Thread(ProcessMailQueue);

       newThread.Start();

       while(!newThread.IsAlive);

       Thread.Sleep(1);

       newThread.Join();              
 }   

 //delay after each batch execution

    private void ProcessMailQueue()
    {

       send the full mails in a batch

        Thread.Sleep(20000);
    }

Any one please give your suggestion....

Answer 1

AFAIK, most of the time, spam detection happens at recipient side i.e. at mail client or service/SMTP managing recipient mailboxes. Its unlikely to happen at originating SMTP (because these days, SMTP needs authentication and/or they does not support relaying so does not need to detect spam).

Regardless, spam detection happens based on many different parameters such as number of recipient (to/cc/bcc), mail contents, a list of know spammer SMTP getaways etc so you have to consider that. Typically, email messages with legitimate content, subject filled, having a valid form, and few recipients (with To specified) are unlikely considered as a spam.