[Exim] Questions about SMTP pipelining

I've got a couple of questions about SMTP pipelining...

First of all, what is it? My understanding is that it's the practice
of sending a whole bunch of SMTP commands all at once without waiting
for a response between each one. Is that right?

Second, do only spammers to this, to exploit the fact that most mail
servers will process all the commands in sequence so the spammer can
move on to the next mail server more quickly?

Thirdly, if it *is* a spamming practice, does Exim automatically see
when it's happening and reject the message? Or is there a way to
configure Exim to do this?

  ____    |\/|                 Brian Kendig   Set your priorities right.
  \  /\   / ..__.    brian at enchanter net   No one ever said on his
   \/  \__\   _/   http://www.enchanter.net/  death bed, "Gee, if I'd
    \__   __  \_      Be insatiably curious.  only spent more time at
       \____\___\           Ask "why" a lot.  the office."