kernel security?

["Chris Evans" <chris@psyctc.sghms.ac.uk>]

I am just shipping off a machine to go into an ISP to act as an 
SMTP, POP3, IMAP, list (superlist), WWW (apacheSSL), ftp and 
possibly IRC server.  Load won't be high but I'd like to minimise 
risks of this leaf positioned machine being used for spoofing and 
forwarding.  I _think_ I'm getting my head around how to use 
sendmail.cf to prevent SMTP forwarding while still allowing proper 
list functioning.  

I think there are configuration options allowing IP forwarding that I 
should turn off in the kernel.  Am I right?  Anyone point me to the 
right info.?

TIA,


Chris