Which type of mail must contain personal information and be mailed in First Class Mail (FCM)?

First Class Mail (FCM) is specifically designed to handle personal and private correspondence, which typically contains sensitive information. This category of mail includes letters, bills, and personal messages that need to be delivered quickly and securely. Unlike other mail classes, First Class Mail offers certain features like tracking and delivery confirmation, making it suitable for items that contain personal data.

In contrast, while Express Mail and Priority Mail also provide faster delivery, they may not encompass the same requirements for personal information. Standard Mail is not suitable for personal or sensitive information because it is predominantly used for advertisements and bulk mail, which do not require the same level of security or confidentiality. Therefore, First Class Mail is specifically mandated for handling personal information, ensuring secure and prompt delivery of such sensitive content.