Most mail of any type that isn't stamped have got 2D barcodes on them with the destination address encoded in them. I think it's a matter of when, not if RM have every last item scanned at every last office it passes through (primary and secondary sort in MCs), maybe scanned to a container and the container scan to a york, which in turn would be scanned to a lorry.
When the new scanning thing finally does come in (no idea why it has been delayed), when any york arrives at a DO, all mail on that york will automatically be deemed to have arrived at the DO