diff --git a/addons/mail/models/mail_activity.py b/addons/mail/models/mail_activity.py
index 42f30788b37..4a29e788d95 100644
--- a/addons/mail/models/mail_activity.py
+++ b/addons/mail/models/mail_activity.py
@@ -276,9 +276,12 @@ class MailActivity(models.Model):
         activity_user = activity.sudo(self.env.user)
         activity_user._check_access('create')
 
-        # check target user has rights on document otherwise we have to prevent activity creation
+        # send a notification to assigned user; in case of manually done activity also check
+        # target has rights on document otherwise we prevent its creation. Automated activities
+        # are checked since they are integrated into business flows that should not crash.
         if activity_user.user_id != self.env.user:
-            activity_user._check_access_assignation()
+            if not activity_user.automated:
+                activity_user._check_access_assignation()
             if not self.env.context.get('mail_activity_quick_update', False):
                 activity_user.action_notify()
 
@@ -298,7 +301,8 @@ class MailActivity(models.Model):
 
         if values.get('user_id'):
             if values['user_id'] != self.env.uid:
-                self._check_access_assignation()
+                to_check = self.filtered(lambda act: not act.automated)
+                to_check._check_access_assignation()
                 if not self.env.context.get('mail_activity_quick_update', False):
                     self.action_notify()
             for activity in self:
diff --git a/addons/test_mail/tests/test_mail_activity.py b/addons/test_mail/tests/test_mail_activity.py
index da55ebed4f7..4b3b2e98922 100644
--- a/addons/test_mail/tests/test_mail_activity.py
+++ b/addons/test_mail/tests/test_mail_activity.py
@@ -39,8 +39,23 @@ class TestActivityRights(TestActivityCommon):
         activity2 = self.test_record.activity_schedule('test_mail.mail_act_test_todo')
         activity2.write({'user_id': self.user_employee.id})
 
-    def test_activity_security_user_noaccess(self):
+    def test_activity_security_user_noaccess_automated(self):
+        def _employee_crash(*args, **kwargs):
+            """ If employee is test employee, consider he has no access on document """
+            recordset = args[0]
+            if recordset.env.uid == self.user_employee.id:
+                raise exceptions.AccessError('Hop hop hop Ernest, please step back.')
+            return DEFAULT
 
+        with patch.object(MailTestActivity, 'check_access_rights', autospec=True, side_effect=_employee_crash):
+            activity = self.test_record.activity_schedule(
+                'test_mail.mail_act_test_todo',
+                user_id=self.user_employee.id)
+
+            activity2 = self.test_record.activity_schedule('test_mail.mail_act_test_todo')
+            activity2.write({'user_id': self.user_employee.id})
+
+    def test_activity_security_user_noaccess_manual(self):
         def _employee_crash(*args, **kwargs):
             """ If employee is test employee, consider he has no access on document """
             recordset = args[0]
@@ -50,11 +65,18 @@ class TestActivityRights(TestActivityCommon):
 
         with patch.object(MailTestActivity, 'check_access_rights', autospec=True, side_effect=_employee_crash):
             with self.assertRaises(exceptions.UserError):
-                activity = self.test_record.activity_schedule(
-                    'test_mail.mail_act_test_todo',
-                    user_id=self.user_employee.id)
+                activity = self.env['mail.activity'].create({
+                    'activity_type_id': self.env.ref('test_mail.mail_act_test_todo').id,
+                    'res_model_id': self.env.ref('test_mail.model_mail_test_activity').id,
+                    'res_id': self.test_record.id,
+                    'user_id': self.user_employee.id,
+                })
 
-            activity2 = self.test_record.activity_schedule('test_mail.mail_act_test_todo')
+            activity2 = self.env['mail.activity'].create({
+                'activity_type_id': self.env.ref('test_mail.mail_act_test_todo').id,
+                'res_model_id': self.env.ref('test_mail.model_mail_test_activity').id,
+                'res_id': self.test_record.id,
+            })
             with self.assertRaises(exceptions.UserError):
                 activity2.write({'user_id': self.user_employee.id})