Hay kilburn, it was probably one-to-one translation from my native language that made it sound sarcastic ! my bad
if anyone needs this, here is how to do it (i think):
open /etc/postfix/main.cf
find section smtpd_recipient_restrictions
add
check_recipient_access hash:/etc/postfix/recipient-custom
somewhere in that section after the checks you want to be applied
create the file you defined ( /etc/postfix/recipient-custom ) and inside it put something like:
SOMEDOMAIN.COM OK
then run postmap[2] /etc/postfix/recipient-custom
reload postfix (to create hash?) ... viola ! (i think) !
useful links:
http://www.postfix.org/postconf.5.html
[2]
http://www.postfix.org/access.5.html