CISA.MS.EXO.10.3 - Email scanning SHALL be capable of reviewing emails after delivery.

Contributed by Michael Soule with Jean-Philippe GeorgeAll contributors →

Overview

Email scanning SHALL be capable of reviewing emails after delivery.

Rationale: As known malware signatures are updated, it is possible for an email to be retroactively identified as containing malware after delivery. By scanning emails, the number of malware-infected in users' mailboxes can be reduced.

Remediation action

1. Sign in to Microsoft 365 Defender.
2. In the left-hand menu, go to Email & Collaboration > Policies & Rules.
3. Select Threat Policies.
4. From the Templated policies section, select Preset Security Policies.
5. Under Standard protection, slide the toggle switch to the right so the text next to the toggle reads Standard protection is on.
6. Under Strict protection, slide the toggle switch to the right so the text next to the toggle reads Strict protection is on.

Note: If the toggle slider in step 5 is grayed out, click on Manage protection settings instead and configure the policy settings according to Use the Microsoft 365 Defender portal to assign Standard and Strict preset security policies to users | Microsoft Learn.

Related links

• Defender admin center - Preset security policies
• Defender admin center - Order and precedence of email protection
• CISA 10 Malware Scanning - MS.EXO.10.3v1
• CISA ScubaGear Rego Reference
• Microsoft Learn - Zero-hour auto purge (ZAP) for malware

Test Metadata

Field	Value
Test ID	CISA.MS.EXO.10.3
Severity	High
Suite	CISA
Product	Exchange Online
Related products	Defender
Feature	Anti-malware
Area	Email and collaboration protection
Resource type	Policy
User impact	Low
Implementation cost	Low
MITRE ATT&CK	T1204.002 Malicious File, T1566.001 Spearphishing Attachment
Supports benchmark	CISA SCuBA Secure Configuration Baselines for Microsoft 365 (version ScubaGear main, 2026-10-11), requirement MS.EXO.10.3
Criticality	SHALL
Upstream requirement	Moved to MS.SECURITYSUITE.1.2v1 (was MS.EXO.10.3v1)
Supports controls	cisa-scuba:MS.EXO.10.3, nist-800-53-r5:SI-3
PowerShell test	Test-MtCisaMalwareZap
Services	ExchangeOnline

Source

• Test: tests/cisa/exchange/Test.CISA.MS.EXO.10.3.ps1
• Documentation: tests/cisa/exchange/Test.CISA.MS.EXO.10.3.md