How did Petunia recognise Dumbledore’s voice?

Question

We have a few questions about the Howler that Dumbledore sent Petunia in the rather chaotic kitchen scene at the beginning of Order of the Phoenix. We even have one that asks why Harry didn’t recognise Dumbledore’s voice.

But how is it that Petunia seemingly did recognise Dumbledore’s voice? There’s nothing very identifying, even to Petunia, about the words “Remember my last”. Once she knows the sender is Dumbledore, she would be able to identify that it’s a reference to his last letter to her (when leaving Harry on her doorstep); but the words themselves won’t help her much in identifying who’s speaking.

Moreover, unlike Harry, there is no reason to believe that Petunia had ever heard Dumbledore’s voice before. She’s never been to Hogwarts; his first letter to her was presumably a regular letter; and he never entered the house or spoke to her when he left Harry on her doorstep.

Of course, Dumbledore was likely the only person in the wizarding community that Petunia had ever communicated with (apart from James and Lily), so thinking about it logically, she should be able to work out that it must be from him—but she seems to react immediately and instinctively, rather than spending time turning it logically over in her head:

An awful voice filled the kitchen, echoing in the confined space, issuing from the burning letter on the table.
    ‘Remember my last, Petunia.’
    Aunt Petunia looked as though she might faint. She sank into the chair beside Dudley, her face in her hands.
_{Order of the Phoenix, ch. 2 “A Peck of Owls”}

So how did Petunia immediately recognise Dumbledore’s voice from the Howler?

Answer 1

It is entirely possible that Petunia had met Dumbledore previously:

"It's real for us," said Snape. "Not for her. But we'll get the letter, you and me."

...

"And will it really come by owl?" Lily whispered.

"Normally," said Snape. "But you're Muggle-born, so someone from the school will have to come and explain to your parents."

(from Deathly Hallows, p. 666)

We've seen this happen before, where Hogwarts staff personally visit young witches and wizards who grew up with Muggles to explain to them about Hogwarts. Hagrid visited Harry; Dumbledore, Deputy Headmaster at the time, visited Riddle. It's reasonable to believe that Dumbledore, McGonagall, and Hagrid divvy up the visits between them, and one day Dumbledore showed up on the Evans' doorstep to tell Lily that she was a witch, and that would have been when Petunia met him.

But why on earth would Petunia remember Dumbledore's voice from a full 24 (Lily turned 11 in 1971; the Howler was delivered in 1995) years ago?

To answer this, we turn to the same link Richard did in his answer, but I would like to offer up a different interpretation. Note that Rowling says there were letters before Dumbledore's last letter (the one left to her with baby Harry on the doorstep), and not after it; in fact, the only way the letter left with baby Harry could have been Dumbledore's "last" would be if it was, in fact, the previous letter Dumbledore had written addressed to Petunia.

What, then, were the letters prior to this last one? To answer that we need only look a couple of pages further:

"You didn't think it was such a freak's school when you wrote to the headmaster and begged him to take you."

Petunia turned scarlet.

"Beg? I didn't beg!"

"I saw his reply. It was very kind."

(from Deathly Hallows, p. 670)

So Petunia sent a letter to Dumbledore, and Dumbledore replied. Note that Lily doesn't say that Petunia wrote to the school, but specifically "wrote to the headmaster," all the more reason to believe that Petunia had met Dumbledore when he came to tell Lily she was a witch.

Thus Petunia not only knew who Dumbledore was, she'd no doubt met him before, and he played quite a role in why Petunia hated her sister so much. Naturally his voice would have stuck in her head.

Answer 2

JKR (on her old website) clarified that Dumbledore and the Dursleys have communicated on several occasions since the delivery of Harry Potter at the Dursley's house. This included an urgent communiqué about Harry's illegal flight to the school in 'Harry Potter and the Chamber of Secrets'

‘Not today, Mr Weasley,’ said Dumbledore. ‘But I must impress upon both of you the seriousness of what you have done. I will be writing to both your families tonight. I must also warn you that if you do anything like this again, I will have no choice but to expel you.’

Given his anger, and the propensity shown by the Dursleys to ignore letters from Hogwarts, it's quite reasonable to assume that Dumbledore would have sent this letter as a howler (complete with his voice) rather than by standard owl post.

What did Dumbledore's Howler to Aunt Petunia mean? ('Remember my last'?)

So: Dumbledore is referring to his last letter, which means, of course, the letter he left upon the Dursleys' doorstep when Harry was one year old. But why then (you may well ask) did he not just say 'remember my letter?' Why did he say my last letter? Why, obviously because there were letters before that…

P.S. It has been suggested that I am wrong in saying that Dumbledore's last letter was the one he left on the doorstep with baby Harry, and that he has sent a letter since then concerning Harry's illegal flight to school. However, both Dumbledore and I differentiate between letters sent to the Dursleys as a couple, and messages directed to Petunia ALONE.

_{^{FAQ: JK Rowling Official Site}}

Answer 3

I have a slightly different take...what if "remember my last" refers to Lily's last wish or action which was to protect her son at all cost and which would have been in the letter that accompanied Harry when he arrived on Petunia's doorstep. Lily's last wish was for Petunia to keep her son safe. It's Dumbledore's voice but it is there to remind Petunia of her promise to uphold her sister's last wish.