A Handwritten Card, Signed and Sealed by the Latest Technology - The New York Times

If that's too time-consuming, check Amazon Beefs Up Gift Receipt Service With Automated Thank You Notes (International Business Times) for details on scanning QR codes to generate thank-you notes

"Receiving a physical, handwritten thank-you note or letter these days feels special, but it also requires some work. “You have to assemble all the pieces,” Mr. Caberwal said — including paper, a pen, the recipient’s address, an envelope and a stamp — and then the note has to be written and mailed, all of which is time-consuming. He wanted to enable people to do that more easily, by harnessing technology to create a product that still felt very personal and worth keeping."

A Handwritten Card, Signed and Sealed by the Latest Technology - The New York Times