My uncle, who does not have a computer and internet access, uses his Amex card to purchase his diabetic supplies. He likes the fact that come tax time, he can get a printout detailing these purchases as supporting documentation for his medical deductions. As I said, he doesn't have a computer, so he used my mother's computer and apparently at one point listed my mother's email address, presumably to receive this report.
Shortly thereafter, my mother, started receiving email alerts every time there was activity with his card, such as a purchase or a payment. Being a private man, this really bothered my uncle. He called their customer no-service several times and they could find no linkage from his account to my mother's email address. They went as far as canceling the account and creating a new one with a new card. Last I heard, my mother still gets alerts regarding his account.