I call greenwashing on this.
"Using a fully electric drone supports Royal Mail's continued drive to reduce emissions associated with our operations, whilst connecting the island communities we deliver to."
"By leveraging drone technology, we are revolutionising mail services in remote communities, providing more efficient and timely delivery, and helping to reduce the requirement for emissions-producing vehicles."
So instead of piggybacking onto the existing ferry services which will continue to run, they are setting up a completely separate means of transporting letters and parcels. This isn't about "reducing emissions", it's about money.