Issue from spamhaus with current Postfix config

[springcomp]

Credits to @chrisblech 🙏

This project shows Postfix configuration that rejects messages coming from blocked domains using the Spamhaus Project public mirror DNSBL infrastructure.

Issue

With the current postfix configuration:

smtpd_recipient_restrictions =
[...]
   reject_rbl_client zen.spamhaus.org,
   permit

...all mails are rejected, with the following message: NOQUEUE: reject: RCPT from <redacted>: 554 5.7.1 Service unavailable; Client host [redacted] blocked using zen.spamhaus.org; Error: open resolver; https://check.spamhaus.org/returnc/pub/46.38.225.230/

Following the provided link, spamhaus says:

• The problem is with the recipient’s email server configuration.
• It is not because you are listed on one of our blocklists.
• This page provides the information required to correct this issue: Using our public mirrors? Check your return codes now.
• To succesfully query Spamhaus via public/open resolvers, there is a FREE service which delivers the intelligence faster and with additional blocklists available to increase catch-rates: Spamhaus Data Query Service