You have to know his email address.

One quick whois lookup, and I found the email he was likely sending from. His site has another email listed, so I did a little digging.

Or,

  $ telnet mailhost.com 25
  HELO myserver.hostname.com 
  MAIL FROM: dustin@dustincurtis.com 
  RCPT TO: post@posterous.com
  DATA
  Subject: Hello
  spam spam
  .
  QUIT

You don't even need to know the command line, you can often do stuff like that just from Outlook.

You don't even need to know Outlook, you can often do stuff like that just from the command line. ;)

Actually that's not going to work. This sort of approach would definitely hit our spoof filters.