Quote Originally Posted by zorro View Post
Wouldn't письмо have to be in the genitive письма because it's the direct object of a negated verb?
The rules of using genitive and accusative with negated verbs are somewhat complicated.
In that particular case, there should be accusative, because the direct object is definite ("the letter").
Here is a detailed description: http://www.evartist.narod.ru/text1/66.htm#%D0%B7_04
Hope it helps.