diff --git a/changelog.d/6714.bugfix b/changelog.d/6714.bugfix
new file mode 100644
index 000000000000..410516694fc6
--- /dev/null
+++ b/changelog.d/6714.bugfix
@@ -0,0 +1 @@
+Fix a bug causing Synapse to not always purge quiet rooms with a low `max_lifetime` in their message retention policies when running the automated purge jobs.
diff --git a/changelog.d/6717.misc b/changelog.d/6717.misc
new file mode 100644
index 000000000000..a2a7776126b0
--- /dev/null
+++ b/changelog.d/6717.misc
@@ -0,0 +1 @@
+Add more logging around message retention policies support.
diff --git a/synapse/config/server.py b/synapse/config/server.py
index 9ac112233b0c..0ec1b0fadd78 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -294,6 +294,14 @@ def read_config(self, config, **kwargs):
             self.retention_default_min_lifetime = None
             self.retention_default_max_lifetime = None
 
+        if self.retention_enabled:
+            logger.info(
+                "Message retention policies support enabled with the following default"
+                " policy: min_lifetime = %s ; max_lifetime = %s",
+                self.retention_default_min_lifetime,
+                self.retention_default_max_lifetime,
+            )
+
         self.retention_allowed_lifetime_min = retention_config.get(
             "allowed_lifetime_min"
         )
diff --git a/synapse/handlers/pagination.py b/synapse/handlers/pagination.py
index 00a6afc963d4..71d76202c93d 100644
--- a/synapse/handlers/pagination.py
+++ b/synapse/handlers/pagination.py
@@ -88,6 +88,8 @@ def __init__(self, hs):
         if hs.config.retention_enabled:
             # Run the purge jobs described in the configuration file.
             for job in hs.config.retention_purge_jobs:
+                logger.info("Setting up purge job with config: %s", job)
+
                 self.clock.looping_call(
                     run_as_background_process,
                     job["interval"],
@@ -130,11 +132,22 @@ def purge_history_for_rooms_in_range(self, min_ms, max_ms):
         else:
             include_null = False
 
+        logger.info(
+            "[purge] Running purge job for %d < max_lifetime <= %d (include NULLs = %s)",
+            min_ms,
+            max_ms,
+            include_null,
+        )
+
         rooms = yield self.store.get_rooms_for_retention_period_in_range(
             min_ms, max_ms, include_null
         )
 
+        logger.debug("[purge] Rooms to purge: %s", rooms)
+
         for room_id, retention_policy in iteritems(rooms):
+            logger.info("[purge] Attempting to purge messages in room %s", room_id)
+
             if room_id in self._purges_in_progress_by_room:
                 logger.warning(
                     "[purge] not purging room %s as there's an ongoing purge running"
@@ -156,7 +169,7 @@ def purge_history_for_rooms_in_range(self, min_ms, max_ms):
 
             stream_ordering = yield self.store.find_first_stream_ordering_after_ts(ts)
 
-            r = yield self.store.get_room_event_after_stream_ordering(
+            r = yield self.store.get_room_event_before_stream_ordering(
                 room_id, stream_ordering,
             )
             if not r:
diff --git a/synapse/rest/admin/__init__.py b/synapse/rest/admin/__init__.py
index a10b4a9b7263..2932fe2123d8 100644
--- a/synapse/rest/admin/__init__.py
+++ b/synapse/rest/admin/__init__.py
@@ -107,7 +107,7 @@ async def on_POST(self, request, room_id, event_id):
 
             stream_ordering = await self.store.find_first_stream_ordering_after_ts(ts)
 
-            r = await self.store.get_room_event_after_stream_ordering(
+            r = await self.store.get_room_event_before_stream_ordering(
                 room_id, stream_ordering
             )
             if not r:
diff --git a/synapse/storage/data_stores/main/stream.py b/synapse/storage/data_stores/main/stream.py
index 140da8dad686..056b25b13a3f 100644
--- a/synapse/storage/data_stores/main/stream.py
+++ b/synapse/storage/data_stores/main/stream.py
@@ -525,8 +525,8 @@ def get_recent_event_ids_for_room(self, room_id, limit, end_token):
 
         return rows, token
 
-    def get_room_event_after_stream_ordering(self, room_id, stream_ordering):
-        """Gets details of the first event in a room at or after a stream ordering
+    def get_room_event_before_stream_ordering(self, room_id, stream_ordering):
+        """Gets details of the first event in a room at or before a stream ordering
 
         Args:
             room_id (str):
@@ -541,15 +541,15 @@ def _f(txn):
             sql = (
                 "SELECT stream_ordering, topological_ordering, event_id"
                 " FROM events"
-                " WHERE room_id = ? AND stream_ordering >= ?"
+                " WHERE room_id = ? AND stream_ordering <= ?"
                 " AND NOT outlier"
-                " ORDER BY stream_ordering"
+                " ORDER BY stream_ordering DESC"
                 " LIMIT 1"
             )
             txn.execute(sql, (room_id, stream_ordering))
             return txn.fetchone()
 
-        return self.db.runInteraction("get_room_event_after_stream_ordering", _f)
+        return self.db.runInteraction("get_room_event_before_stream_ordering", _f)
 
     @defer.inlineCallbacks
     def get_room_events_max_id(self, room_id=None):