Why are there 397 queues in Exchange 2003 on SBS 2003?

The other day this client called me claiming that no emails were going out. I noticed they had Exchange configured to send mail out to a smart host. What is a smart host anyway? I changed it to send mail out using DNS and that seemed to get mail flowing again. I do realize that there are other consequences of me changing that setting - in fact I've dealt with this very same problem but it's been so long ago that I don't recall the exact sequence of steps required to clean up Exchange and get their mail flow secure and healthy again.  

I just completed the test to see if their server was an open relay and it passed the test. I don't know what new features Exchange 2003 has over 2000 but I just need to know how to get these queues cleaned up. Right now I don't know how many of these email message are bogus but I'm guessing most of them are. Thanks for any help - they're breathing down my neck now.....   :)