diff --git a/inventory/service/host_vars/lists01.opendev.org.yaml b/inventory/service/host_vars/lists01.opendev.org.yaml
index 7c41f7a3f5..e0d7df254f 100644
--- a/inventory/service/host_vars/lists01.opendev.org.yaml
+++ b/inventory/service/host_vars/lists01.opendev.org.yaml
@@ -31,6 +31,9 @@ exim_aliases:
   product-wg-owner: spam
   user-committee-owner: spam
   spam: ':fail: delivery temporarily disabled due to ongoing spam flood'
+  # This is the local username for mailman processes, but it does not send nor
+  # need to receive messages.
+  mailman: ':blackhole: this address does not accept email'
   # TODO It would be better to bypass verification for postorius@listdomain
   # and set a :fail: rule for anyone trying to send email to this addr.
   # But that requires updating our main exim config so that needs more thought.
diff --git a/playbooks/zuul/files/host_vars/lists99.opendev.org.yaml b/playbooks/zuul/files/host_vars/lists99.opendev.org.yaml
index 860afa0305..ae041aac2b 100644
--- a/playbooks/zuul/files/host_vars/lists99.opendev.org.yaml
+++ b/playbooks/zuul/files/host_vars/lists99.opendev.org.yaml
@@ -40,6 +40,9 @@ exim_aliases:
   product-wg-owner: spam
   user-committee-owner: spam
   spam: ':fail: delivery temporarily disabled due to ongoing spam flood'
+  # This is the local username for mailman processes, but it does not send nor
+  # need to receive messages.
+  mailman: ':blackhole: this address does not accept email'
   # TODO It would be better to bypass verification for postorius@listdomain
   # and set a :fail: rule for anyone trying to send email to this addr.
   # But that requires updating our main exim config so that needs more thought.