Although the sums involved are very small in terms of its annual turnover, the Royal Mail says the proceeds are used to recoup part of the cost of its National Return Letter Centre based in Belfast, which aims to return undeliverable items to the sender wherever possible.

BBC: How much does Royal Mail make from undelivered parcels?

If you ask me, I think Elvis said it best about such messages: Return to sender, address unknown, no such number, no such zone.

FORBES: Elvis Presley Had It Right When It Came To Insider Trading