Postfix’ built-in restriction classes are processed in the following order:
smtpd_client_restrictions
smtpd_helo_restrictions
smtpd_sender_restrictions
smtpd_recipient_restrictions
smtpd_data_restrictions
regardless of the order in which they’re listed in main.cf. Restrictions (within a restriction class) are evaluated in the order in which they’re listed.
Processing within a restriction class ends on the first match.
Useful link: http://www.postfix.org/RESTRICTION_CLASS_README.html#external