diff --git a/app/dao/service_letter_contact_dao.py b/app/dao/service_letter_contact_dao.py
new file mode 100644
index 000000000..578483f62
--- /dev/null
+++ b/app/dao/service_letter_contact_dao.py
@@ -0,0 +1,45 @@
+from app import db
+from app.dao.dao_utils import transactional
+from app.errors import InvalidRequest
+from app.models import ServiceLetterContact
+
+
+def dao_get_letter_contacts_by_service_id(service_id):
+    letter_contacts = db.session.query(
+        ServiceLetterContact
+    ).filter(
+        ServiceLetterContact.service_id == service_id
+    ).order_by(
+        ServiceLetterContact.created_at
+    ).all()
+
+    return letter_contacts
+
+
+def create_or_update_letter_contact(service_id, contact_block):
+    letter_contacts = dao_get_letter_contacts_by_service_id(service_id)
+    if len(letter_contacts) == 0:
+        letter_contact = ServiceLetterContact(
+            service_id=service_id,
+            contact_block=contact_block
+        )
+        dao_create_letter_contact(letter_contact)
+    elif len(letter_contacts) == 1:
+        letter_contacts[0].contact_block = contact_block
+        dao_update_letter_contact(letter_contacts[0])
+    else:
+        # Once we move allowing letter contact blocks, this method will be removed
+        raise InvalidRequest(
+            "Multiple letter contacts were found, this method should not be used.",
+            status_code=500
+        )
+
+
+@transactional
+def dao_create_letter_contact(letter_contact):
+    db.session.add(letter_contact)
+
+
+@transactional
+def dao_update_letter_contact(letter_contact):
+    db.session.add(letter_contact)
diff --git a/app/service/rest.py b/app/service/rest.py
index 48f1e6f44..909675df5 100644
--- a/app/service/rest.py
+++ b/app/service/rest.py
@@ -140,15 +140,16 @@ def update_service(service_id):
     # Capture the status change here as Marshmallow changes this later
     service_going_live = fetched_service.restricted and not req_json.get('restricted', True)
 
-    if 'reply_to_email_address' in req_json:
-        create_or_update_email_reply_to(fetched_service.id, req_json['reply_to_email_address'])
-
     current_data = dict(service_schema.dump(fetched_service).data.items())
     current_data.update(request.get_json())
     update_dict = service_schema.load(current_data).data
+    dao_update_service(update_dict)
+
+    if 'reply_to_email_address' in req_json:
+        create_or_update_email_reply_to(fetched_service.id, req_json['reply_to_email_address'])
+
     if 'sms_sender' in req_json:
         insert_or_update_service_sms_sender(fetched_service, req_json['sms_sender'])
-    dao_update_service(update_dict)
 
     if service_going_live:
         send_notification_to_service_users(
diff --git a/tests/app/dao/test_service_letter_contact_dao.py b/tests/app/dao/test_service_letter_contact_dao.py
new file mode 100644
index 000000000..770fdfa16
--- /dev/null
+++ b/tests/app/dao/test_service_letter_contact_dao.py
@@ -0,0 +1,66 @@
+import pytest
+
+from app.dao.service_letter_contact_dao import (
+    create_or_update_letter_contact,
+    dao_get_letter_contacts_by_service_id,
+)
+from app.errors import InvalidRequest
+from app.models import ServiceLetterContact
+from tests.app.db import create_letter_contact, create_service
+
+
+def test_dao_get_letter_contacts_by_service_id(notify_db_session):
+    service = create_service()
+    default_letter_contact = create_letter_contact(service=service, contact_block='Edinburgh, ED1 1AA')
+    another_letter_contact = create_letter_contact(service=service, contact_block='Cardiff, CA1 2DB')
+
+    results = dao_get_letter_contacts_by_service_id(service_id=service.id)
+
+    assert len(results) == 2
+    assert default_letter_contact in results
+    assert another_letter_contact in results
+
+
+def test_create_or_update_letter_contact_creates_new_entry(notify_db_session):
+    service = create_service()
+
+    create_or_update_letter_contact(service.id, 'Cardiff, CA1 2DB')
+
+    letter_contacts = dao_get_letter_contacts_by_service_id(service.id)
+
+    assert ServiceLetterContact.query.count() == 1
+    assert letter_contacts[0].service.id == service.id
+    assert letter_contacts[0].contact_block == 'Cardiff, CA1 2DB'
+
+
+def test_create_or_update_letter_contact_does_not_create_another_entry(notify_db_session):
+    service = create_service()
+    create_letter_contact(service, 'London, NW1 2DB')
+    create_or_update_letter_contact(service.id, 'Bristol, BR1 2DB')
+
+    letter_contacts = dao_get_letter_contacts_by_service_id(service.id)
+
+    assert len(letter_contacts) == 1
+
+
+def test_create_or_update_letter_contact_updates_existing_entry(notify_db_session):
+    service = create_service()
+    create_letter_contact(service, 'London, NW1 2DB')
+
+    create_or_update_letter_contact(service.id, 'Bristol, BR1 2DB')
+
+    letter_contact = dao_get_letter_contacts_by_service_id(service.id)
+
+    assert len(letter_contact) == 1
+    assert letter_contact[0].service.id == service.id
+    assert letter_contact[0].contact_block == 'Bristol, BR1 2DB'
+
+
+def test_create_or_update_letter_contact_raises_exception_if_multiple_contact_blocks_exist(notify_db_session):
+    service = create_service()
+    create_letter_contact(service=service, contact_block='Edinburgh, ED1 1AA')
+    create_letter_contact(service=service, contact_block='Manchester, MA1 2BB', is_default=False)
+
+    with pytest.raises(expected_exception=InvalidRequest) as e:
+        create_or_update_letter_contact(service_id=service.id, contact_block='Swansea, SN1 3CC')
+    assert e.value.message == "Multiple letter contacts were found, this method should not be used."