Yes, I did read it. It was affecting all recipients on all domains.
I’ve noticed today that the zen.spamhaus.org check for inbound mail is also failing for a very similar reason which looks like it has elements in common with this topic. For example:
Aug 30 09:25:10 mail postfix/smtpd[12160]: NOQUEUE: reject: RCPT from mail-wr1-f46.google.com[209.85.221.46]: 554 5.7.1 Service
unavailable; Client host [209.85.221.46] blocked using zen.spamhaus.org; Error: open resolver; https://www.spamhaus.org/returnc/
pub/172.71.129.38; from=<user@gmail.com> to=<user@example.com> proto=ESMTP helo=<mail-wr1-f46.google.com>
That failing IP is gmail! If I remove reject_rbl_client zen.spamhaus.org from my main.cf, it works again. Is spamhaus becoming especially unreliable recently?