I have a personal grudge against Royal Mail, at Birthdays and the like, we wouldn't get money that people had sent in cards. Visits to my Grandmas would sometimes go along the lines of
"So, what did you splend your birthday money on?"
"...What birthday money?"
Thankfully this isn't an isolted case of senility, because it happens with other friends and relatives, unless there is a large and elaborate conspiracy asunder.
In the post, a card is obviously a card, in their bright envelpoes and springy tactileness, and of course someone had noticed the interesting habit of cards to have money in, and was helping themselves to our post. Now relatives send cheques or wait till they see us in person. A few months ago, a postal worker at the Eccles office which supplies our post was charged with theiving birthday cards and the like.