We need to send out 1500 emails, but our host (in common with many other hosts) block bulk emails if more than 500 per hour are sent out.

Many people do not realise that their hosts do this, and receive no warning that their emails haven't been sent (our host phoned us up and told us last time).

With this in mind, is there a way to slow down the sending of emails from the Newsletter module?

I thought that adding the sleep() command would work, but don't know where to put it.

The file that you are looking for is NewsletterEmailProcess.php

After the line of code that reads '$newsletter->write();' [line 119]

add the sleep command.... so it looks like this:

   $newsletter->ParentID = $this->newsletter->ID;
      $newsletter->write();
      sleep(8);