What type of correspondence involves sending messages to more than one recipient simultaneously?

The type of correspondence that involves sending messages to multiple recipients simultaneously is known as a joint letter. This format is commonly used in situations where a unified message needs to be communicated to various individuals or groups, such as in a collaborative effort or when addressing a collective issue. A joint letter is typically signed by multiple authors or parties who present a cohesive viewpoint, making it an effective means of communication when a message needs to reach several recipients at once.

In contrast, the other options cater to different contexts or purposes. Personal notes are typically intended for individual recipients and do not aim for simultaneous distribution. Directive memos are often internal communications that provide instructions or guidelines to specific individuals or departments rather than a broader audience. Feedback letters are generally one-on-one communications that convey responses or evaluations and are not designed for mass distribution.