To detect unauthorized disclosure of confidential documents sent over corporate email, monitoring all emails based on pre-defined criteria is the best approach. This involves setting up automated monitoring systems that analyze email content, attachments, and metadata to identify any potential unauthorized disclosures. By defining specific criteria (such as keywords related to confidential information), organizations can proactively detect and prevent leaks. Requiring encryption before sending documents (option A) is important but does not address monitoring for unauthorized disclosures. Firewalls (option B) protect the network but do not specifically focus on email content. Reporting outgoing emails marked as confidential (option C) relies on user self-reporting and may not catch all incidents12. References: 1(https://www.isaca.org/resources/isaca- journal/past-issues/2010/data-governance-for-privacy-confidentiality-and-compliance-a-holistic-approach) 2 (https://www.isaca.org/resources/news-and-trends/newsletters/atisaca/2020/volume-6/best-practices-for- privacy-audits)

The first step in an incident response plan is typically preparation12. However, among the options provided, validating the incident would be the first step. This involves confirming that a security event is actually an incident3. It's important to verify the event to avoid wasting resources on false positives.
References:
* Incident Response Plan: Frameworks and Steps - CrowdStrike
* What is Incident Response? Plan and Steps | Microsoft Security
* What Are the Phases of an Incident Response Plan? - ISC2 Blog

Unstructured data is data that does not have a predefined model or organization, making it difficult to store, process, and analyze using traditional relational databases or spreadsheets. Unstructured data can pose a risk to an organization if it contains sensitive, confidential, or regulated information that is not properly secured, managed, or governed. To minimize the risk of unstructured data, the first step is to identify the repositories of unstructured data, such as file servers, cloud storage, email systems, social media platforms, etc. This will help to understand the scope, volume, and nature of unstructured data in the organization, and to prioritize the areas that need further analysis and action. References: Unstructured data - Wikipedia