What was in the letter to the Dursleys Dumbledore left with baby Harry?

Question

What was in the letter to the Dursleys Dumbledore left with baby Harry?

_{What did the Howler to Aunt Petunia in Order of the Phoenix mean? is related to this question, but it is not the same question. The answer to the first question is that Dumbledore sends Petunia a Howler, telling her to remember his last letter, which is the letter he left with Harry as an infant. I am asking what was in the letter left with baby Harry? I could not find this question when I did my due diligence; I hope it is not a duplicate.}

Is there any information about this? In Order of the Phoenix, Vernon attempts to throw Harry out of the house following the dementor attack on Harry and Dudley, and Dumbledore sends a Howler:

‘You can open it if you like,’ said Harry, ‘but I’ll hear what it says anyway. That’s a Howler. [SNIP] Open it!’ Harry urged her. ‘Get it over with! It’ll happen anyway.’

‘No.’

Aunt Petunia’s hand was trembling. She looked wildly around the kitchen as though looking for an escape route, but too late – the envelope burst into flames. Aunt Petunia screamed and dropped it.

An awful voice filled the kitchen, echoing in the confined space, issuing from the burning letter on the table.

‘Remember my last, Petunia.’

_{Order of the Phoenix - page 40-41 - Bloomsbury - chapter two, A Peck of Owls}

What was in that last letter? I feel sure this has been addressed, but I cannot find it. What did Dumbledore write to the Dursleys that convinced such awful people to take in and care for (take that with a grain of salt) a hated and unwanted relative?

Answer 1

The best I can think of right now comes from this post-Deathly Hallows interview:

What did Dumbledore write in the letter to make the Dursleys take Harry?

As you know, as we find out in book seven, Petunia once really wanted to be part of that world. And you discover that Dumbledore has written to her prior to the Howler… Dumbledore wrote to her very kindly and explained why he couldn't let her come to Hogwarts to become a witch.

So, Petunia, much as she denies it afterwards, much as she turns against that world when she met Uncle Vernon, who is the biggest anti-wizard you could ever met in your life, a tiny part of her, and that's the part that almost wished Harry luck when she said goodbye to him in this book, she just teetered on the verge of saying, “I do know what you're up against and I hope it's OK”.

But she couldn't bring herself to say it. Years of pretending she doesn't care have hardened her. But Dumbledore appealed in the letter you're asking about, so that part of Petunia that did remember wanting desperately to be part of the world and he appealed to her sense of fair play to a sister that she had hated because Lily had what she couldn't have. So that's how she persuaded Petunia to keep Harry. Good question.

— J.K. Rowling at Carnegie Hall, October 2007

So essentially he appealed to Petunia’s better nature, and her jealousy and love for her sister. For all she envied Lily, I think the scenes from Snape’s memories show that she did love her, and since Harry is Lily’s only child, she might have been persuaded to take him in.

We also know that Dumbledore gave her at least a cursory explanation of Lily’s sacrifice, and how Harry would be safer with her than anywhere else. In Order of the Phoenix, Dumbledore mentions part of the letter to Harry:

“While you can still call home the place where your mother’s blood dwells, there you cannot be touched or harmed by Voldemort. He shed her blood, but it lives on in you and her sister. Her blood became your refuge. You need return there only once a year, but as long as you can still call it home, there he cannot hurt you. Your aunt knows this. I explained what I had done in the letter I left, with you, on her doorstep. She knows that allowing you houseroom may well have kept you alive for the past fifteen years.”

— Order of the Phoenix, chapter 37, The Lost Prophecy

This means that he also must have given details of Voldemort and the First Wizarding War, and the potential danger to Harry. Petunia has some idea of the dangers of dark creatures (such as Dementors), and may have noticed the effects of the First War in the Muggle world. Dumbledore probably gave her more of an idea of the threat than she ever lets on.