What type of correspondence includes multiple-address letters?

The correct choice pertains to official correspondence, which is defined by its formal nature and adherence to established guidelines and protocols. Official correspondence often involves communication that is generated and exchanged within or between organizations, such as military branches, government entities, or other official bodies.

Multiple-address letters are a distinct aspect of official correspondence because they are used when a message needs to reach several recipients simultaneously, highlighting the collective nature of the communication. This format is efficient and ensures that all parties receive the same information at the same time, which is crucial in maintaining clarity and consistency in official matters.

In contrast, personal correspondence typically involves private exchanges between individuals and does not usually incorporate multiple addresses or the formal structure required by official communication. Informal messages tend to be casual and may lack the structured format important for properly conveying official information. Simplified notes, while possibly brief and direct, do not encompass the broader scope or formal requirements of correspondence addressed to multiple parties.