smtpd_restriction_classes = check_ips

smtpd_recipient_restrictions = check_recipient_access hash:/something, reject_unauth_destination

/something:
@domain1.com	check_ips
@domain2.com	check_ips

check_ips = check_client_access hash:/something2

/something2
1.2.3.4 OK
1.2.3.5 NOT OK