Your organization has a Microsoft 365 subscription.

The correct answer is A. the Microsoft Defender portal . Microsoft documents that phishing investigation and analysis for email threats is handled in Microsoft Defender for Office 365 through the Microsoft Defender portal . Microsoft’s phishing investigation guidance and email security reporting both point admins to Defender capabilities such as Threat Explorer , campaign views , and phish reports to understand the scope, affected users, and impact of phishing attacks.

The other options are not the primary investigation tool for this scenario. The Microsoft 365 admin center is mainly for tenant administration and usage reporting, not detailed phishing impact investigation. The Microsoft Entra admin center focuses on identity and access management, not email threat analysis. The Exchange admin center manages mail flow and Exchange settings, but Microsoft’s current phishing investigation workflows are centered in the Microsoft Defender portal , where security analysts can review detections, remediation actions, and affected recipients.

So, to review the impact of a phishing incident that targeted email users, the Microsoft-documented choice is the Microsoft Defender portal .