I just banged my head against delivery problems for a bit and discovered that I had added a spamhaus RBL, then deleted it, but that it wasn’t removed completely from main.cf so it was essentially partially enabled.

smtpd_client_restrictions = permit_mynetworks sbl-xbl.spamhaus.org permit

Of course, this was a test environment, and no mail was actually lost, but is this a known issue? I hadn’t seen it mentioned anywhere.