What types of mail pieces are included in Standard mail?

Standard mail includes items like booklets, catalogs, and lightweight merchandise because this category is designed for bulk mail and advertising materials that are not particularly time-sensitive. Standard mail is typically used for promotional materials and does not require special handling or expedited delivery. This type of mail is intended for the general public and is often characterized by its cost-effectiveness, making it suitable for sending large volumes of materials at lower rates.

Personal letters and postcards are generally classified differently, often falling under First-Class mail. Packages and freight also do not qualify as Standard mail, as they usually require different service levels due to their size and handling needs. Certified and registered mail are services that provide additional security and tracking for important documents, which also distinguishes them from Standard mail.

Thus, the inclusion of booklets, catalogs, and lightweight merchandise in Standard mail is appropriate due to their promotional nature and the bulk mailing option they provide.