Thanks to Tom for sending me a reminder about the Scouts and Guides Christmas Post. At 20p per card it beats the competitors by a long long way.
You just drop your cards and money in the white boxes provided – like the one pictured at Charity Christmas Cards in the Bear Room at the Guildhall.
The Scouts, Guides, and other helpers do the rest. They collect the cards from all the white boxes, sort them in their own temporary sorting office, and the deliverers make sure they get to the correct address.