You can point your mail server at dnsbl.mxo.michaelspost.com for a DNSBL.
It will return a code of 127.0.0.2 for any blocked IP.
A line of postfix config for the smtpd_recipient_restrictions section might be:
reject_rbl_client dnsbl.mxo.michaelspost.com=127.0.0.2

You might notice that the timestamps on some rows are all the same. I've been gathering the data for quite some time, but only recently started tracking the timestamp.