What type of correspondence is typically maintained in a centralized filing system?

The correct answer focuses on the maintenance of only official copies of outgoing correspondence in a centralized filing system. Centralized filing systems are designed to retain important documents that serve legal, administrative, and historical purposes. By keeping official copies of outgoing correspondence, organizations ensure that they have a formal record of communications that reflect the entity's decisions, commitments, and actions.

This practice promotes accountability and helps in tracking the correspondence for future reference. Retaining only official copies means that the system stays organized and enhances efficiency by preventing clutter from unnecessary documents. This selective retention helps in managing space and resources effectively.

The other answer choices encompass broader categories of documents that are not typically centralized in the same manner. For instance, maintaining all copies of correspondence would lead to an unmanageable volume and difficulty in tracking essential information. Incoming correspondence is often processed differently, potentially handled by various departments. Similarly, classifying all correspondence as classified would contradict the nature of centralized filing, which is generally for official correspondence that requires ongoing access, rather than strictly securing classified information.