Linuxconfig generates a sendmail.cf file based on sendmail version 8.8, but
the binary is 8.9. This allows people to use your server as a relay by
simply doing the following:

To: "someone"@yourdomain.com

If someone sends an email to the above address your mail server will relay
the message to "someone". This is true even if you have
ip_allow or pop_auth configured. This problem will get you on the blacklist
in a flash!

I'm no sendmail expert. In fact, I don't have a clue where to begin to fix
this. My server is full production and I can't afford to bring everything
down trying to figure out how the m4 program works. The book sendmail by
O'reilly 2nd addition is just as cryptic as everything else I've found
regarding sendmail.