All forwarding has been restored. Queues of Delivery Receipts have now been cleared. Delivery receipts are forwarding in their usual. We'll continue to monitor. We apologise for any inconvenience. :)

We have investigated and identified an issue where delivery receipts are not being forwarded to user's web-hooks (if supplied). Delivery receipts are being recorded and are processing - but not forwarding.
This therefore only affects users that have a Delivery Receipt forwarding web-hook setup. These Delivery Receipts are being queued and will be processed.