diff --git a/paperwork/api.py b/paperwork/api.py
index a2fc114..53455bb 100644
--- a/paperwork/api.py
+++ b/paperwork/api.py
@@ -22,6 +22,63 @@ class DepartmentViewSet(viewsets.ModelViewSet):
     queryset = Department.objects.all()
     serializer_class = DepartmentSerializer
 
+    @action(detail=False, methods=["get"])
+    def mailing_lists(self, request, format=None):
+        """
+        Generate a mailing list for each department, containing all
+        certified users for tools in that department or child departments
+        """
+        departments = self.queryset.prefetch_related(
+            "children",
+            "list_moderator_flag",
+            Prefetch(
+                "certificationdefinition_set__certificationversion_set__certification_set__member",
+                queryset=Member.objects.with_is_active(),
+            ),
+        )
+        lists = {}
+        for department in departments:
+            if department.list_moderator_flag is not None:
+                moderator_emails = department.list_moderator_flag.members.values_list(
+                    "email", flat=True
+                )
+            else:
+                moderator_emails = []
+
+            # TODO: this could be done in SQL instead if
+            #       membershipworks was in the same database
+            active_certified_members = {
+                member_cert.member.sanitized_mailbox
+                for certification in department.certificationdefinition_set.all()
+                for version in certification.certificationversion_set.all()
+                for member_cert in version.certification_set.all()
+                if member_cert.member and member_cert.member.is_active
+            }
+
+            lists[department.list_name] = {
+                "real_name": department.list_name,
+                "moderator": moderator_emails,
+                "subject_prefix": f"[CMS {department.name}] ",
+                "reply_to_address": department.list_reply_to_address,
+                "members": active_certified_members,
+            }
+
+        # Add child departments' members to their parents
+        # TODO: this seems wildly inefficient
+        def recurse_children(department):
+            for child in department.children.all():
+                recurse_children(child)
+
+                lists[department.list_name]["members"] |= lists[child.list_name][
+                    "members"
+                ]
+
+        for department in departments:
+            if department.parent_id is None:
+                recurse_children(department)
+
+        return Response(lists)
+
 
 class CertificationDefinitionSerializer(serializers.HyperlinkedModelSerializer):
     class Meta:
@@ -33,32 +90,6 @@ class CertificationDefinitionViewSet(viewsets.ModelViewSet):
     queryset = CertificationDefinition.objects.all()
     serializer_class = CertificationDefinitionSerializer
 
-    @action(detail=False, methods=["get"])
-    def mailing_lists(self, request, format=None):
-        """
-        Generate a mailing list for each certification definition,
-        containing all certified users for that tool
-        """
-        lists = {}
-        for definition in self.queryset.exclude(mailing_list="").prefetch_related(
-            Prefetch(
-                "certificationversion_set__certification_set__member",
-                queryset=Member.objects.with_is_active(),
-            ),
-        ):
-            if definition.mailing_list not in lists:
-                lists[definition.mailing_list] = set()
-            # TODO: this could be done in sql instead; was planning to
-            # maybe also filter to only active certs
-            for version in definition.certificationversion_set.all():
-                for cert in version.certification_set.all():
-                    if cert.member and cert.member.is_active:
-                        lists[definition.mailing_list].add(
-                            cert.member.sanitized_mailbox
-                        )
-
-        return Response(lists)
-
 
 class CertificationVersionSerializer(serializers.HyperlinkedModelSerializer):
     class Meta: