Royal Mail was the name of a British postal company. (TV: Day One)
The TARDIS narrowly missed crashing in to one of the company's vans. (TV: The Christmas Invasion)
One of their workers was nearly murdered by the Sex Gas in the host body of Carys Fletcher. (TV: Day One)
Another postman heard Owen Harper being shouted at by Ed Morgan. (TV: Ghost Machine)
A Royal Mail card was stolen by the staff of Torchwood Three. (TV: Children of Earth: Day Three)
One of the storage bags was seen on the Thames House helipad. (TV: Children of Earth: Day Five)
Behind the scenes
In 2013, to celebrate Doctor Who's 50th anniversary, Royal Mail published the Doctor Who 50th Anniversary Royal Mail Prestige Stamp Book, a stamp book which included the Eleventh Doctor comic story Doctor Who and the Last Stand.