Which type of mail is categorized under special handling?

Registered mail is categorized under special handling due to the additional security measures and tracking options it provides. This type of mail is typically used for sending important or valuable items, ensuring that they are securely transported and that there is a verifiable record of their transmission. Registered mail is handled separately from regular mail and is often treated with greater care during processing and delivery, which is essential for items that are high in value or require specific delivery protocols.

In contrast, first-class mail is a standard category for most time-sensitive letters and postcards, bulk mail refers to large quantities of mail at reduced rates mainly for marketing purposes, and expedited mail, while faster than standard delivery options, does not necessarily have the same level of security and tracking as registered mail. Special handling is primarily concerned with the security and meticulous tracking associated with the transmission of registered items, making it a distinct category from the others listed.