Which of the following is not a service offered by USPS?

Air Mail is not a service currently offered by USPS in the same traditional sense as it was in the past. Historically, Air Mail involved sending letters by air transportation, but over time, the postal service streamlined its offerings. Now, USPS utilizes different classes of mail that effectively encompass air transport without explicitly branding it as "Air Mail." Services like Priority Mail and Priority Mail Express have features that ensure swift delivery similar to what Air Mail used to provide, but they do not carry the Air Mail designation.

In contrast, Media Mail is a Special Service for shipping educational materials at a lower rate, Library Mail is designed for sending books and other materials between libraries, and Parcel Select is a service specific to bulk shipping options for commercial customers. All these options remain active services within the USPS framework, differentiating them from the obsolescence of the Air Mail category.