A few years ago, I had some postcard style Christmas cards printed, and and hand wrote the addresses on the cards.. and the PO machinery sorted every dang one of them back to my "from" address since it was more easily read by the machines, despite the fact that it was tiny and the hand-written "TO" addresses were large and very legible, and very obvious to any human.

I was ticked... because I had sent out nearly 100 cards that year. I had no luck even getting the PO to refund my postage.. ultimately I put every card in an envelope and paid more to send them. I was not a happy postal customer.

What's even stupider is that not all of them came back right away - they seemed to come back in batches over about a week, starting the day after they were originally mailed.