whitelisting

Any suggestions on how to whitelist a email sender address that is
occasionally getting blocked due to a RBL hit for the sending
servers IP?

I have tried below, but I keep finding that it does not work and I
keep having to comment out the last two RBLs.

smtpd_sender_restrictions = 
    check_recipient_access hash:/usr/local/etc/postfix/access.smtpd_sender_restrictions,
    reject_rbl_client bl.spamcop.net,
    reject_rhsbl_sender rhsbl.sorbs.net,
    reject_rbl_client sbl-xbl.spamhaus.org,
    reject_rbl_client smtp.dnsbl.sorbs.net,
    reject_rbl_client virbl.dnsbl.bit.nl,
    reject_rbl_client virus.rbl.msrbl.net,
    reject_rbl_client web.dnsbl.sorbs.net,
    reject_rbl_client spam.dnsbl.sorbs.net,
    reject_rbl_client dnsbl-2.uceprotect.net,
    reject_rbl_client dnsbl-3.uceprotect.net