FWIW, mail receipts are an artifact of AOL in the early 1990s. Their propensity to annoy far outweigh their benefit. My suggestion to you is to leave the 1990s in the 1990s.
The most important thing about receipts is that provide no actionable information. As a general proposition, they don't work between domains. Even in the case where they do "work," they are a big case of "so what?" All they tell you is that someone opened your message. They don't tell you that they were actually read. And they don't tell you by whom. Despite the fact that you have a receipt, your intended recipient denies having received an important message. What are you going to do about it?