Exchange Online Mail Flow Security: Anti-Spam, Inbound Phishing & Routing Rules
Hardening default Exchange Online Protection (EOP) policies to block zero-day lures, impersonation attempts, and unauthorized relaying.
Overcoming Default EOP Permissiveness
Default Exchange Online Protection configurations allow a high percentage of sophisticated phishing lures to pass into user inboxes. To combat targeted attacks, organizations must tune anti-phishing policies to enforce strict mailbox intelligence and user impersonation protection.
Hardening Inbound Anti-Spam and Quarantine
Configure inbound spam filters to automatically quarantine high-confidence phishing and malware messages rather than routing them to Junk Email folders where employees can still open malicious links. Restrict quarantine release permissions so only security analysts can inspect quarantined items.
Enforcing Strict Connector Rules
Audit all inbound and outbound Exchange connectors. Ensure hybrid email connectors enforce mandatory TLS encryption and domain subject name verification to prevent unauthorized mail relaying through tenant infrastructure.
Related Articles & Advisories
Microsoft 365 Security Baseline: Essential Defensive Hardening Before Audits
A technical walkthrough of default misconfigurations in Microsoft 365 and Entra ID, and the practical controls needed to prevent business email compromise and identity takeover.
Architecting Zero-Trust Conditional Access in Entra ID for Modern Workforces
A deep dive into constructing modular, non-conflicting Conditional Access policies that enforce least-privilege context without locking out legitimate personnel.
Defeating Adversary-in-the-Middle (AiTM) Phishing & Session Token Theft
How modern reverse proxy toolkits steal active browser session cookies and bypass standard SMS/TOTP MFA, and the specific controls needed to prevent token replay.