Which USPS service would likely be unsuitable for sending items that contain sensitive information?

First-Class Mail is generally considered unsuitable for sending items containing sensitive information due to its lack of enhanced security features. This service offers standard delivery and does not include tracking or insurance options, making it more vulnerable to loss or theft.

In contrast, services like Registered Mail provide a high level of security, including detailed tracking, insurance coverage, and strict handling protocols designed for valuable or sensitive items. Express Mail and Priority Mail also offer features such as tracking and more reliable delivery times but are not as secure as Registered Mail. Therefore, when sending sensitive information, it is essential to choose a service that prioritizes security and tracking, making options like Registered Mail a more suitable choice compared to First-Class Mail.