From "http://www.orbs.org/otherresources.cgi", we find that:
Linuxconf users beware! - Linuxconf was found to be
generating faulty (old) check_rcpt tables as recently
as 20 July 1999. Make sure your version is newer
than this before using it to generate sendmail.cf files.
As a result, using linuxconf opens you to acting as an open
smtp relay. My site is getting hit hard by the spammers...
Added Jacques to CC line
1.16r10-2 released, which should fix this.