こんな嵐の中、まさかここまで郵便を届けにくるやつはいまい、と思っているにちがいない。
He was surely thinking that nobody would deliver mail here in a storm like this. (my TL)
I cannot work out what いまい is doing in this sentence.
I've come across まい as a negative volitional form before, but I'm assuming it is attached to the verb いる here and that doesn't seem like a verb you could make volitional.
To me it would make perfect sense if I replaced いまい with いない (is this true?), so maybe it's just a typo.