[CentOS] postfix and mail origin checks

hi,

Whats the 'robust' way to make sure email to a specific destination is 
only accepted if it came over the localhost:25 or /usr/sbin/sendmail 
route ? anything else should get a 5xx error. Emails to other 
destinations should remain unaffected.

Using postfix/c4. Had a look around, and header_checks might be one way 
to go.

-- 
Karanbir Singh : http://www.karan.org/  : 2522219 at icq