diff --git a/app/dao/notifications_dao.py b/app/dao/notifications_dao.py
index 7544dfdea..1229d3940 100644
--- a/app/dao/notifications_dao.py
+++ b/app/dao/notifications_dao.py
@@ -44,7 +44,8 @@ from app.models import (
     NOTIFICATION_SENT,
     SMS_TYPE,
     EMAIL_TYPE,
-    ServiceDataRetention
+    ServiceDataRetention,
+    Service
 )
 from app.utils import get_london_midnight_in_utc
 from app.utils import midnight_n_days_ago, escape_special_characters
@@ -315,8 +316,10 @@ def _filter_query(query, filter_dict=None):
 
 
 @statsd(namespace="dao")
-@transactional
-def delete_notifications_created_more_than_a_week_ago_by_type(notification_type):
+def delete_notifications_created_more_than_a_week_ago_by_type(notification_type, qry_limit=10000):
+    current_app.logger.info(
+        'Deleting {} notifications for services with flexible data retention'.format(notification_type))
+
     flexible_data_retention = ServiceDataRetention.query.filter(
         ServiceDataRetention.notification_type == notification_type
     ).all()
@@ -329,16 +332,39 @@ def delete_notifications_created_more_than_a_week_ago_by_type(notification_type)
         if notification_type == LETTER_TYPE:
             _delete_letters_from_s3(query)
         deleted += query.delete(synchronize_session='fetch')
+        db.session.commit()
+
+    current_app.logger.info(
+        'Deleting {} notifications for services without flexible data retention'.format(notification_type))
 
     seven_days_ago = convert_utc_to_bst(datetime.utcnow()).date() - timedelta(days=7)
     services_with_data_retention = [x.service_id for x in flexible_data_retention]
-    query = db.session.query(Notification).filter(func.date(Notification.created_at) < seven_days_ago,
-                                                  Notification.notification_type == notification_type,
-                                                  Notification.service_id.notin_(
-                                                      services_with_data_retention))
-    if notification_type == LETTER_TYPE:
-        _delete_letters_from_s3(query=query)
-    deleted += query.delete(synchronize_session='fetch')
+    service_ids_to_purge = db.session.query(Service.id).filter(Service.id.notin_(services_with_data_retention)).all()
+
+    for service_id in service_ids_to_purge:
+        subquery = db.session.query(
+            Notification
+        ).filter(
+            Notification.notification_type == notification_type,
+            func.date(Notification.created_at) < seven_days_ago,
+            Notification.service_id == service_id
+        ).limit(qry_limit)
+
+        if notification_type == LETTER_TYPE:
+            _delete_letters_from_s3(query=subquery)
+
+        number_deleted = db.session.query(Notification).filter(
+            Notification.id.in_([x.id for x in subquery.all()])).delete(synchronize_session='fetch')
+        deleted += number_deleted
+        db.session.commit()
+        while number_deleted > 0:
+            number_deleted = db.session.query(Notification).filter(
+                Notification.id.in_([x.id for x in subquery.all()])).delete(synchronize_session='fetch')
+            deleted += number_deleted
+            db.session.commit()
+
+    current_app.logger.info('Finished deleting {} notifications'.format(notification_type))
+
     return deleted
 
 
diff --git a/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py b/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
index 1479921bd..4b3d8c9e8 100644
--- a/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
+++ b/tests/app/dao/notification_dao/test_notification_dao_delete_notifications.py
@@ -182,10 +182,24 @@ def test_delete_notifications_does_try_to_delete_from_s3_when_letter_has_not_bee
 
     create_notification(template=letter_template, status='sending',
                         reference='LETTER_REF')
-    delete_notifications_created_more_than_a_week_ago_by_type('email')
+    delete_notifications_created_more_than_a_week_ago_by_type('email', qry_limit=1)
     mock_get_s3.assert_not_called()
 
 
+def test_delete_notifications_calls_subquery(
+        notify_db_session, mocker
+):
+    service = create_service()
+    sms_template = create_template(service=service)
+    create_notification(template=sms_template, created_at=datetime.now() - timedelta(days=8))
+    create_notification(template=sms_template, created_at=datetime.now() - timedelta(days=8))
+    create_notification(template=sms_template, created_at=datetime.now() - timedelta(days=8))
+
+    assert Notification.query.count() == 3
+    delete_notifications_created_more_than_a_week_ago_by_type('sms', qry_limit=1)
+    assert Notification.query.count() == 0
+
+
 def _create_templates(sample_service):
     email_template = create_template(service=sample_service, template_type='email')
     sms_template = create_template(service=sample_service)