the original is correct too

The speaker just says LETTERS if they know there are letters for them, and ANY LETTERS if they don’t know.

If somebody knows there are letters, why would they ask this question then??

Say you’re a teacher and you usually pick up your mail at the main office. You run into one of the secretaries in the cafeteria and she tells you she saw some letters for you. You go to the main office and say “Are there (some) letters for me?” because you’re not so much asking IF you have any letters, you confirming that there ARE letters for you.

Now is clear! Got it. Thanks!

👍🏼