diff --git a/app/service/send_notification.py b/app/service/send_notification.py
index b80baf770..a00d151a4 100644
--- a/app/service/send_notification.py
+++ b/app/service/send_notification.py
@@ -1,5 +1,6 @@
 from sqlalchemy.orm.exc import NoResultFound
 
+from app import create_random_identifier
 from app.config import QueueNames
 from app.dao.notifications_dao import _update_notification_status
 from app.dao.service_email_reply_to_dao import dao_get_reply_to_by_id
@@ -37,6 +38,12 @@ def validate_created_by(service, created_by_id):
         raise BadRequestError(message=message)
 
 
+def create_one_off_reference(template_type):
+    if template_type == LETTER_TYPE:
+        return create_random_identifier()
+    return None
+
+
 def send_one_off_notification(service_id, post_data):
     service = dao_fetch_service_by_id(service_id)
     template = dao_get_template_by_id_and_service_id(
@@ -77,7 +84,8 @@ def send_one_off_notification(service_id, post_data):
         api_key_id=None,
         key_type=KEY_TYPE_NORMAL,
         created_by_id=post_data['created_by'],
-        reply_to_text=reply_to
+        reply_to_text=reply_to,
+        reference=create_one_off_reference(template.template_type),
     )
 
     queue_name = QueueNames.PRIORITY if template.process_type == PRIORITY else None
diff --git a/tests/app/service/test_send_one_off_notification.py b/tests/app/service/test_send_one_off_notification.py
index f8ffdf28a..0c20611dc 100644
--- a/tests/app/service/test_send_one_off_notification.py
+++ b/tests/app/service/test_send_one_off_notification.py
@@ -10,7 +10,9 @@ from app.config import QueueNames
 from app.dao.service_whitelist_dao import dao_add_and_commit_whitelisted_contacts
 from app.service.send_notification import send_one_off_notification
 from app.models import (
+    EMAIL_TYPE,
     KEY_TYPE_NORMAL,
+    LETTER_TYPE,
     MOBILE_TYPE,
     PRIORITY,
     SMS_TYPE,
@@ -64,13 +66,17 @@ def test_send_one_off_notification_calls_celery_correctly(persist_mock, celery_m
     )
 
 
-def test_send_one_off_notification_calls_persist_correctly(
+def test_send_one_off_notification_calls_persist_correctly_for_sms(
     persist_mock,
     celery_mock,
     notify_db_session
 ):
     service = create_service()
-    template = create_template(service=service, content="Hello (( Name))\nYour thing is due soon")
+    template = create_template(
+        service=service,
+        template_type=SMS_TYPE,
+        content="Hello (( Name))\nYour thing is due soon",
+    )
 
     post_data = {
         'template_id': str(template.id),
@@ -91,7 +97,92 @@ def test_send_one_off_notification_calls_persist_correctly(
         api_key_id=None,
         key_type=KEY_TYPE_NORMAL,
         created_by_id=str(service.created_by_id),
-        reply_to_text='testing'
+        reply_to_text='testing',
+        reference=None,
+    )
+
+
+def test_send_one_off_notification_calls_persist_correctly_for_email(
+    persist_mock,
+    celery_mock,
+    notify_db_session
+):
+    service = create_service()
+    template = create_template(
+        service=service,
+        template_type=EMAIL_TYPE,
+        subject="Test subject",
+        content="Hello (( Name))\nYour thing is due soon",
+    )
+
+    post_data = {
+        'template_id': str(template.id),
+        'to': 'test@example.com',
+        'personalisation': {'name': 'foo'},
+        'created_by': str(service.created_by_id)
+    }
+
+    send_one_off_notification(service.id, post_data)
+
+    persist_mock.assert_called_once_with(
+        template_id=template.id,
+        template_version=template.version,
+        recipient=post_data['to'],
+        service=template.service,
+        personalisation={'name': 'foo'},
+        notification_type=EMAIL_TYPE,
+        api_key_id=None,
+        key_type=KEY_TYPE_NORMAL,
+        created_by_id=str(service.created_by_id),
+        reply_to_text=None,
+        reference=None,
+    )
+
+
+def test_send_one_off_notification_calls_persist_correctly_for_letter(
+    mocker,
+    persist_mock,
+    celery_mock,
+    notify_db_session
+):
+    mocker.patch(
+        'app.service.send_notification.create_random_identifier',
+        return_value='this-is-random-in-real-life',
+    )
+    service = create_service()
+    template = create_template(
+        service=service,
+        template_type=LETTER_TYPE,
+        subject="Test subject",
+        content="Hello (( Name))\nYour thing is due soon",
+    )
+
+    post_data = {
+        'template_id': str(template.id),
+        'to': 'First Last',
+        'personalisation': {
+            'name': 'foo',
+            'address line 1': 'First Last',
+            'address line 2': '1 Example Street',
+            'postcode': 'SW1A 1AA',
+        },
+        'created_by': str(service.created_by_id)
+    }
+
+    send_one_off_notification(service.id, post_data)
+
+    persist_mock.assert_called_once_with(
+        template_id=template.id,
+        template_version=template.version,
+        recipient=post_data['to'],
+        service=template.service,
+        personalisation=post_data['personalisation'],
+        notification_type=LETTER_TYPE,
+        api_key_id=None,
+        key_type=KEY_TYPE_NORMAL,
+        created_by_id=str(service.created_by_id),
+        reply_to_text=None,
+        reference='this-is-random-in-real-life',
     )