diff --git a/addons/microsoft_calendar/controllers/main.py b/addons/microsoft_calendar/controllers/main.py
index 5a4d218091b..400324de722 100644
--- a/addons/microsoft_calendar/controllers/main.py
+++ b/addons/microsoft_calendar/controllers/main.py
@@ -53,6 +53,7 @@ class MicrosoftCalendarController(CalendarController):
                 })
 
             # If App authorized, and user access accepted, We launch the synchronization
+            sync_context.update({'dont_notify': True})
             need_refresh = request.env.user.sudo().with_context(sync_context)._sync_microsoft_calendar()
 
             # If synchronization has been stopped or paused
diff --git a/addons/microsoft_calendar/models/calendar.py b/addons/microsoft_calendar/models/calendar.py
index b46705888dd..b7c5b2adeee 100644
--- a/addons/microsoft_calendar/models/calendar.py
+++ b/addons/microsoft_calendar/models/calendar.py
@@ -61,7 +61,7 @@ class Meeting(models.Model):
             time_offset = timedelta(minutes=5)
             domain = expression.AND([domain, [('write_date', '>=', self.env.user.microsoft_last_sync_date - time_offset)]])
 
-        self.env['calendar.event'].search(domain).write({
+        self.env['calendar.event'].with_context(dont_notify=True).search(domain).write({
             'need_sync_m': True,
         })
 
diff --git a/addons/microsoft_calendar/tests/test_update_events.py b/addons/microsoft_calendar/tests/test_update_events.py
index b87ba70e899..72bf1af2548 100644
--- a/addons/microsoft_calendar/tests/test_update_events.py
+++ b/addons/microsoft_calendar/tests/test_update_events.py
@@ -4,6 +4,7 @@ from dateutil.parser import parse
 import logging
 import pytz
 from unittest.mock import patch, ANY
+from freezegun import freeze_time
 
 from odoo import Command
 
@@ -1393,3 +1394,14 @@ class TestUpdateEvents(TestCommon):
                          "The event organizer must be user B (self.attendee_user) after the event organizer update.")
         self.assertTrue(self.attendee_user.partner_id.id in new_event.partner_ids.ids,
                         "User B (self.attendee_user) should be listed as attendee after the event organizer update.")
+
+    @freeze_time('2021-09-22')
+    @patch.object(MicrosoftCalendarService, 'patch')
+    def test_restart_sync_with_synced_recurrence(self, mock_patch):
+        """ Ensure that sync restart is not blocked when there are recurrence outliers in Odoo database. """
+        # Stop synchronization, set recurrent events as outliers and restart sync with Outlook.
+        self.organizer_user.stop_microsoft_synchronization()
+        self.recurrent_events.with_user(self.organizer_user).write({'microsoft_id': False, 'follow_recurrence': False})
+        self.attendee_user.with_user(self.attendee_user).restart_microsoft_synchronization()
+        self.organizer_user.with_user(self.organizer_user).restart_microsoft_synchronization()
+        self.assertTrue(all(ev.need_sync_m for ev in self.recurrent_events))