testing postfix' maps_rbl config?

[Neale Banks]

I've set up postfix on a Woody machine as a low-volume server (like it's
getting *really* low volume).  All appears well except the amount of mail
slipping through the maps_rbl config, which is pretty draconian - like
this:

#
# OK, we are being pretty aggresive here....
maps_rbl_domains = proxies.blackholes.wirehub.net.,
                dnsbl.njabl.org.,
                query.bondedsender.org.,
                bl.spamcop.net.,
                relays.ordb.org.,
                inputs.relays.osirusoft.com.
smtpd_client_restrictions = hash:/etc/postfix/spammers,
                hash:/etc/postfix/kr-nets,
                reject_maps_rbl,
                permit
#

/etc/postfix/spammers and /etc/postfix/kr-nets only have entries for which
teh RHS is "550 <blah>".

Any suggestions on why sites which are listed in the above RBLs would be
able to relay mail (as in for domains handled by this server) through the
above rules?

Any suggestions on how to explicitly test the RBL config?

Thanks,
Neale.