active_send_mail = 0
threshold = 20

for (each email in the list) {
  send_email(address, content)

  # make sure we don't fork too many processes
  active_send_mail = active_send_mail + 1
  if (active_send_mail >= threshold) {
    waitpid -1
    active_send_mail --
    report on status
  }
}

sub send_email
{
  fork
  if child {
    send_the_email using mail or Net::SMTP
    exit
  }
  # in parent
  return child pid
}