Microsoft will make it easier for Defender for Office 365 customers to identify users and domains targeted in impersonation-based phishing attacks. Security admins will be able to use new filters dubbed Impersonation user and Impersonated domain together with the Threat Explorer and real-time detections. Microsoft also added priority protection for accounts of high-profile employees including executive-level managers who are frequently targeted in attacks. Microsoft is working on making it generally available worldwide in all environments by the end of February.
Source: https://www.bleepingcomputer.com/news/security/office-365-will-help-admins-find-impersonation-attack-targets/