reject_rhsbl_client rbl_domain=d.d.d.d reject_rhsbl_helo rbl_domain=d.d.d.dHow does postfix submit the query to the rbl_domain?Prepend the reversed client IP address to the provider's domain (without =d.d.d.d). See RFC5782 or https://en.wikipedia.org/wiki/DNSBL. Postfix was implemented long before these documents were written, but the basic principle hasn't changed.
But this is the hostname version reject_rhsbl_*, wouldn't it submit hostname and not an IP?