、、。
At the post office, mail is sorted by destination.
Literal
Post-office [at-では], mail [topic-は], destination [according-to-に応じて] sort-[passive-される].
~に応じて ('according to, in response to, depending on') is a useful connective for formal register. The whole sentence has a textbook's explanatory rhythm. Note that the passive 分類される is impersonal — there's no agent, just the fact that the mail gets sorted. This neutral-observational frame is classic expository writing.