diff --git a/changelog.d/3670.feature b/changelog.d/3670.feature
new file mode 100644
index 0000000000..ba00f2d2ec
--- /dev/null
+++ b/changelog.d/3670.feature
@@ -0,0 +1 @@
+Where server is disabled, block ability for locked out users to read new messages
diff --git a/changelog.d/3692.bugfix b/changelog.d/3692.bugfix
new file mode 100644
index 0000000000..f44e13dca1
--- /dev/null
+++ b/changelog.d/3692.bugfix
@@ -0,0 +1 @@
+Fix missing yield in synapse.storage.monthly_active_users.initialise_reserved_users
diff --git a/synapse/api/auth.py b/synapse/api/auth.py
index 9c62ec4374..18c73f0549 100644
--- a/synapse/api/auth.py
+++ b/synapse/api/auth.py
@@ -775,15 +775,25 @@ class Auth(object):
             )
 
     @defer.inlineCallbacks
-    def check_auth_blocking(self):
+    def check_auth_blocking(self, user_id=None):
         """Checks if the user should be rejected for some external reason,
         such as monthly active user limiting or global disable flag
+
+        Args:
+            user_id(str|None): If present, checks for presence against existing
+            MAU cohort
         """
         if self.hs.config.hs_disabled:
             raise AuthError(
                 403, self.hs.config.hs_disabled_message, errcode=Codes.HS_DISABLED
             )
         if self.hs.config.limit_usage_by_mau is True:
+            # If the user is already part of the MAU cohort
+            if user_id:
+                timestamp = yield self.store.user_last_seen_monthly_active(user_id)
+                if timestamp:
+                    return
+            # Else if there is no room in the MAU bucket, bail
             current_mau = yield self.store.get_monthly_active_count()
             if current_mau >= self.hs.config.max_mau_value:
                 raise AuthError(
diff --git a/synapse/handlers/sync.py b/synapse/handlers/sync.py
index 6393a9674b..3b21a04a5d 100644
--- a/synapse/handlers/sync.py
+++ b/synapse/handlers/sync.py
@@ -191,6 +191,7 @@ class SyncHandler(object):
         self.clock = hs.get_clock()
         self.response_cache = ResponseCache(hs, "sync")
         self.state = hs.get_state_handler()
+        self.auth = hs.get_auth()
 
         # ExpiringCache((User, Device)) -> LruCache(state_key => event_id)
         self.lazy_loaded_members_cache = ExpiringCache(
@@ -198,19 +199,27 @@ class SyncHandler(object):
             max_len=0, expiry_ms=LAZY_LOADED_MEMBERS_CACHE_MAX_AGE,
         )
 
+    @defer.inlineCallbacks
     def wait_for_sync_for_user(self, sync_config, since_token=None, timeout=0,
                                full_state=False):
         """Get the sync for a client if we have new data for it now. Otherwise
         wait for new data to arrive on the server. If the timeout expires, then
         return an empty sync result.
         Returns:
-            A Deferred SyncResult.
+            Deferred[SyncResult]
         """
-        return self.response_cache.wrap(
+        # If the user is not part of the mau group, then check that limits have
+        # not been exceeded (if not part of the group by this point, almost certain
+        # auth_blocking will occur)
+        user_id = sync_config.user.to_string()
+        yield self.auth.check_auth_blocking(user_id)
+
+        res = yield self.response_cache.wrap(
             sync_config.request_key,
             self._wait_for_sync_for_user,
             sync_config, since_token, timeout, full_state,
         )
+        defer.returnValue(res)
 
     @defer.inlineCallbacks
     def _wait_for_sync_for_user(self, sync_config, since_token, timeout,
diff --git a/synapse/storage/monthly_active_users.py b/synapse/storage/monthly_active_users.py
index 9a6e699386..7e417f811e 100644
--- a/synapse/storage/monthly_active_users.py
+++ b/synapse/storage/monthly_active_users.py
@@ -46,7 +46,7 @@ class MonthlyActiveUsersStore(SQLBaseStore):
                 tp["medium"], tp["address"]
             )
             if user_id:
-                self.upsert_monthly_active_user(user_id)
+                yield self.upsert_monthly_active_user(user_id)
                 reserved_user_list.append(user_id)
             else:
                 logger.warning(
@@ -125,7 +125,7 @@ class MonthlyActiveUsersStore(SQLBaseStore):
         # is racy.
         # Have resolved to invalidate the whole cache for now and do
         # something about it if and when the perf becomes significant
-        self._user_last_seen_monthly_active.invalidate_all()
+        self.user_last_seen_monthly_active.invalidate_all()
         self.get_monthly_active_count.invalidate_all()
 
     @cached(num_args=0)
@@ -164,11 +164,11 @@ class MonthlyActiveUsersStore(SQLBaseStore):
             lock=False,
         )
         if is_insert:
-            self._user_last_seen_monthly_active.invalidate((user_id,))
+            self.user_last_seen_monthly_active.invalidate((user_id,))
             self.get_monthly_active_count.invalidate(())
 
     @cached(num_args=1)
-    def _user_last_seen_monthly_active(self, user_id):
+    def user_last_seen_monthly_active(self, user_id):
         """
             Checks if a given user is part of the monthly active user group
             Arguments:
@@ -185,7 +185,7 @@ class MonthlyActiveUsersStore(SQLBaseStore):
             },
             retcol="timestamp",
             allow_none=True,
-            desc="_user_last_seen_monthly_active",
+            desc="user_last_seen_monthly_active",
         ))
 
     @defer.inlineCallbacks
@@ -197,7 +197,7 @@ class MonthlyActiveUsersStore(SQLBaseStore):
             user_id(str): the user_id to query
         """
         if self.hs.config.limit_usage_by_mau:
-            last_seen_timestamp = yield self._user_last_seen_monthly_active(user_id)
+            last_seen_timestamp = yield self.user_last_seen_monthly_active(user_id)
             now = self.hs.get_clock().time_msec()
 
             # We want to reduce to the total number of db writes, and are happy
diff --git a/tests/handlers/test_sync.py b/tests/handlers/test_sync.py
new file mode 100644
index 0000000000..8c8b65e04e
--- /dev/null
+++ b/tests/handlers/test_sync.py
@@ -0,0 +1,71 @@
+# -*- coding: utf-8 -*-
+# Copyright 2018 New Vector Ltd
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+from twisted.internet import defer
+
+from synapse.api.errors import AuthError, Codes
+from synapse.api.filtering import DEFAULT_FILTER_COLLECTION
+from synapse.handlers.sync import SyncConfig, SyncHandler
+from synapse.types import UserID
+
+import tests.unittest
+import tests.utils
+from tests.utils import setup_test_homeserver
+
+
+class SyncTestCase(tests.unittest.TestCase):
+    """ Tests Sync Handler. """
+
+    @defer.inlineCallbacks
+    def setUp(self):
+        self.hs = yield setup_test_homeserver(self.addCleanup)
+        self.sync_handler = SyncHandler(self.hs)
+        self.store = self.hs.get_datastore()
+
+    @defer.inlineCallbacks
+    def test_wait_for_sync_for_user_auth_blocking(self):
+
+        user_id1 = "@user1:server"
+        user_id2 = "@user2:server"
+        sync_config = self._generate_sync_config(user_id1)
+
+        self.hs.config.limit_usage_by_mau = True
+        self.hs.config.max_mau_value = 1
+
+        # Check that the happy case does not throw errors
+        yield self.store.upsert_monthly_active_user(user_id1)
+        yield self.sync_handler.wait_for_sync_for_user(sync_config)
+
+        # Test that global lock works
+        self.hs.config.hs_disabled = True
+        with self.assertRaises(AuthError) as e:
+            yield self.sync_handler.wait_for_sync_for_user(sync_config)
+        self.assertEquals(e.exception.errcode, Codes.HS_DISABLED)
+
+        self.hs.config.hs_disabled = False
+
+        sync_config = self._generate_sync_config(user_id2)
+
+        with self.assertRaises(AuthError) as e:
+            yield self.sync_handler.wait_for_sync_for_user(sync_config)
+        self.assertEquals(e.exception.errcode, Codes.MAU_LIMIT_EXCEEDED)
+
+    def _generate_sync_config(self, user_id):
+        return SyncConfig(
+            user=UserID(user_id.split(":")[0][1:], user_id.split(":")[1]),
+            filter_collection=DEFAULT_FILTER_COLLECTION,
+            is_guest=False,
+            request_key="request_key",
+            device_id="device_id",
+        )
diff --git a/tests/storage/test_client_ips.py b/tests/storage/test_client_ips.py
index fa60d949ba..c2e88bdbaf 100644
--- a/tests/storage/test_client_ips.py
+++ b/tests/storage/test_client_ips.py
@@ -63,7 +63,7 @@ class ClientIpStoreTestCase(tests.unittest.TestCase):
         yield self.store.insert_client_ip(
             user_id, "access_token", "ip", "user_agent", "device_id"
         )
-        active = yield self.store._user_last_seen_monthly_active(user_id)
+        active = yield self.store.user_last_seen_monthly_active(user_id)
         self.assertFalse(active)
 
     @defer.inlineCallbacks
@@ -79,7 +79,7 @@ class ClientIpStoreTestCase(tests.unittest.TestCase):
         yield self.store.insert_client_ip(
             user_id, "access_token", "ip", "user_agent", "device_id"
         )
-        active = yield self.store._user_last_seen_monthly_active(user_id)
+        active = yield self.store.user_last_seen_monthly_active(user_id)
         self.assertFalse(active)
 
     @defer.inlineCallbacks
@@ -87,13 +87,13 @@ class ClientIpStoreTestCase(tests.unittest.TestCase):
         self.hs.config.limit_usage_by_mau = True
         self.hs.config.max_mau_value = 50
         user_id = "@user:server"
-        active = yield self.store._user_last_seen_monthly_active(user_id)
+        active = yield self.store.user_last_seen_monthly_active(user_id)
         self.assertFalse(active)
 
         yield self.store.insert_client_ip(
             user_id, "access_token", "ip", "user_agent", "device_id"
         )
-        active = yield self.store._user_last_seen_monthly_active(user_id)
+        active = yield self.store.user_last_seen_monthly_active(user_id)
         self.assertTrue(active)
 
     @defer.inlineCallbacks
@@ -102,7 +102,7 @@ class ClientIpStoreTestCase(tests.unittest.TestCase):
         self.hs.config.max_mau_value = 50
         user_id = "@user:server"
 
-        active = yield self.store._user_last_seen_monthly_active(user_id)
+        active = yield self.store.user_last_seen_monthly_active(user_id)
         self.assertFalse(active)
 
         yield self.store.insert_client_ip(
@@ -111,5 +111,5 @@ class ClientIpStoreTestCase(tests.unittest.TestCase):
         yield self.store.insert_client_ip(
             user_id, "access_token", "ip", "user_agent", "device_id"
         )
-        active = yield self.store._user_last_seen_monthly_active(user_id)
+        active = yield self.store.user_last_seen_monthly_active(user_id)
         self.assertTrue(active)
diff --git a/tests/storage/test_monthly_active_users.py b/tests/storage/test_monthly_active_users.py
index 0a2c859f26..511acbde9b 100644
--- a/tests/storage/test_monthly_active_users.py
+++ b/tests/storage/test_monthly_active_users.py
@@ -33,7 +33,7 @@ class MonthlyActiveUsersTestCase(tests.unittest.TestCase):
 
     @defer.inlineCallbacks
     def test_initialise_reserved_users(self):
-
+        self.hs.config.max_mau_value = 5
         user1 = "@user1:server"
         user1_email = "user1@matrix.org"
         user2 = "@user2:server"
@@ -60,9 +60,9 @@ class MonthlyActiveUsersTestCase(tests.unittest.TestCase):
 
         # Test user is marked as active
 
-        timestamp = yield self.store._user_last_seen_monthly_active(user1)
+        timestamp = yield self.store.user_last_seen_monthly_active(user1)
         self.assertTrue(timestamp)
-        timestamp = yield self.store._user_last_seen_monthly_active(user2)
+        timestamp = yield self.store.user_last_seen_monthly_active(user2)
         self.assertTrue(timestamp)
 
         # Test that users are never removed from the db.
@@ -86,17 +86,18 @@ class MonthlyActiveUsersTestCase(tests.unittest.TestCase):
         self.assertEqual(1, count)
 
     @defer.inlineCallbacks
-    def test__user_last_seen_monthly_active(self):
+    def test_user_last_seen_monthly_active(self):
         user_id1 = "@user1:server"
         user_id2 = "@user2:server"
         user_id3 = "@user3:server"
-        result = yield self.store._user_last_seen_monthly_active(user_id1)
+
+        result = yield self.store.user_last_seen_monthly_active(user_id1)
         self.assertFalse(result == 0)
         yield self.store.upsert_monthly_active_user(user_id1)
         yield self.store.upsert_monthly_active_user(user_id2)
-        result = yield self.store._user_last_seen_monthly_active(user_id1)
+        result = yield self.store.user_last_seen_monthly_active(user_id1)
         self.assertTrue(result > 0)
-        result = yield self.store._user_last_seen_monthly_active(user_id3)
+        result = yield self.store.user_last_seen_monthly_active(user_id3)
         self.assertFalse(result == 0)
 
     @defer.inlineCallbacks