What service allows a customer to obtain street-addressed mail from the post office when the customer regularly receives 50 letters or more on the first delivery trip?

The correct response to the question is the service known as "Firm holdout." This service is specifically designed to cater to businesses or individuals who receive a large volume of mail regularly. Under this service, customers can have their street-addressed mail held at the post office for pickup, which is especially useful when they do not require regular delivery or are unable to receive their mail at the usual address.

In this scenario, the indication that the customer receives 50 letters or more on the first delivery trip aligns perfectly with the intent behind the Firm holdout service. It facilitates a more organized and efficient way for the customer to retrieve a significant quantity of mail at their convenience, rather than having it delivered to an address that may not be consistently occupied.

Other services mentioned in the choices cater to different needs. General delivery is primarily for individuals who do not have a permanent address. Hold Mail is used when a customer wants their mail temporarily held during their absence, which would not apply here since the customer is typically receiving a high volume of mail. Caller service, while similar, is generally used for mail not being delivered due to various reasons, and it is more focused on businesses than residential customers.