if message too big to put on high volume queue then save to queue

SQS fails if the message body is over 256kb. Normally our messages are
quite small, but if we're using the new save-api-email task with an
email that has a large body, we can get over that limit. If so, handle
the exception and fall back to the existing code path (saving to the
database and sending a deliver-email task, which only has a notification
id.

app/v2/notifications/post_notifications.py

@@ -3,6 +3,7 @@ import functools
 import uuid
 from datetime import datetime
 
+from boto.exception import SQSError
 from flask import request, jsonify, current_app, abort
 from notifications_utils.recipients import try_validate_and_format_phone_number
 
@@ -187,6 +188,7 @@ def post_notification(notification_type):
 
 
 def process_sms_or_email_notification(*, form, notification_type, api_key, template, service, reply_to_text=None):
+    notification_id = None
     form_send_to = form['email_address'] if notification_type == EMAIL_TYPE else form['phone_number']
 
     send_to = validate_and_format_recipient(send_to=form_send_to,
@@ -209,19 +211,29 @@ def process_sms_or_email_notification(*, form, notification_type, api_key, templ
         # To take the pressure off the db for API requests put the notification for our high volume service onto a queue
         # the task will then save the notification, then call send_notification_to_queue.
         # We know that this team does not use the GET request, but relies on callbacks to get the status updates.
-        notification = save_email_to_queue(
-            form=form,
-            notification_type=notification_type,
-            api_key=api_key,
-            template=template,
-            service_id=service.id,
-            personalisation=personalisation,
-            document_download_count=document_download_count,
-            reply_to_text=reply_to_text
-        )
-        return notification
+        try:
+            notification_id = uuid.uuid4()
+            notification = save_email_to_queue(
+                form=form,
+                notification_id=str(notification_id),
+                notification_type=notification_type,
+                api_key=api_key,
+                template=template,
+                service_id=service.id,
+                personalisation=personalisation,
+                document_download_count=document_download_count,
+                reply_to_text=reply_to_text
+            )
+            return notification
+        except SQSError:
+            # if SQS cannot put the task on the queue, it's probably because the notification body was too long and it
+            # went over SQS's 256kb message limit. If so, we
+            current_app.logger.info(
+                f'Notification {notification_id} failed to save to high volume queue. Using normal flow instead'
+            )
 
     notification = persist_notification(
+        notification_id=notification_id,
         template_id=template.id,
         template_version=template.version,
         recipient=form_send_to,
@@ -255,6 +267,7 @@ def process_sms_or_email_notification(*, form, notification_type, api_key, templ
 
 def save_email_to_queue(
     *,
+    notification_id,
     form,
     notification_type,
     api_key,
@@ -265,7 +278,7 @@ def save_email_to_queue(
     reply_to_text=None
 ):
     data = {
-        "id": str(uuid.uuid4()),
+        "id": notification_id,
         "template_id": str(template.id),
         "template_version": template.version,
         "to": form['email_address'],