Quickly Diagnose Issues with Email Threat Policies
The Microsoft 365 commercial support team resolves customer support cases and provides support to help you be successful and realize the full potential and value of your purchase. Our support services extend across the entire lifecycle and include pre-sales, onboarding and deployment, usage and management, accounts and billing, and break-fix support. We also spend a considerable amount of time working to improve the supportability of Microsoft 365 services to reduce the number of issues you experience as well as minimize the effort and time it takes to resolve your issues if they do occur.
Today, we’re excited to share some insights on working with Exchange Online Protection (EOP) and Microsoft Defender for Office 365 (MDO).
Exchange Online Protection (EOP) and Microsoft Defender for Office 365 (MDO) provide cumulative layers of email security that include multiple threat policies. Some organizations choose our quick, “set-and-forget” preset policies, while others choose to customize their email threat policies for different sets of users, groups, domains and business requirements.
Determine your protection policy strategy.
Which policies apply to which recipients?
In Microsoft Customer Service and Support (CSS), we often hear from administrators who create custom policies and find it challenging to determine which threat policy applied to a user or a message, especially if the recipient is part of multiple groups or policies. Consistent and effective policy management can lower administrator overhead, confusion, and even security risks, (e.g. bad emails being delivered to users due to overrides, or good emails being blocked because of aggressive blocks.) With that, we’re happy to announce two new tools to help you diagnose policy issues quickly and efficiently!
Introducing: Email Threat Policy Diagnostic for a Recipient
Requirements: Network Message ID, Recipient address
Run the Email Threat Policy Diagnostic as an administrator in any admin portal (Microsoft 365 Admin Center, Microsoft Defender XDR, Exchange Admin Center, Compliance portal, etc.).
The quick link https://aka.ms/diagmdopolicy will 1) open the Microsoft 365 Admin Center and 2) prepopulate the Get Help field (“?”) with the diagnostic query.
Provide a Network Message ID and a recipient address for the Email Threat Policy diagnostic to show which policies applied when the message was received, and what policies covered the recipient.
Example 1: Testing Safe Links user exclusions
Your organization has three Safe Links policies defined. Joe works in the Threat Intelligence department, which commonly requires access for testing malicious links from email messages in a virtual environment. You decide to exclude Joe from Custom and Built-in policies to skip Safe Links processing.
Upon further testing, Joe still sees Safe Links applied to email messages with malicious URLs. After you collect a Network Message ID from Joe’s last test message, run the Email Threat Policy diagnostic. In this example, we will use these two pieces of input:
Network Message ID: 42715389-04ae-4577-d1a3-08dcbad6af8a
Recipient email address: [email protected]
From the results, you’ll learn that the Standard Preset Security policy applied to this message. This is because Standard and Strict preset security policies take precedence over any custom and built-in policies and apply to your entire organization. To learn more about policy order and processing, see https://aka.ms/mdoorder.
Solution and validation:
Since your organization requires a higher degree of customizations, you decide to turn the Standard Preset Security policy Off 
Now that you only have two policies remaining (Custom and Built-in), and Joe is excluded from both, new test messages go through bypassing Safe Links.
Example 2: Testing why anti-malware policies fire on excluded attachments
You have multiple malware filtering policies that block different file attachments. The Custom malware policy is your latest policy that blocks all media file types, such as .mov, .mp4 and .mp3.
Joe stopped getting voicemail messages. You know your voicemail provider uses an .mp3 file type and upon investigation, you find these messages are quarantined unexpectedly. You collect the Network Message ID and recipient address and run the Email Threat Policy diagnostic to verify which policy is applied to the message.
Solution and validation:
Since the custom policy was recently defined to block all media file types, you decide to modify the policy and remove .mp3 from the list of restricted file types. To confirm, you can run the diagnostics using the Network Message ID from the quarantine, provide Joe’s recipient address, and find out that the “Custom Malware policy” applies.
Why Network Message ID (NMID)?
A network message ID is a unique message ID value that persists across copies of the message that may be created due to bifurcation or distribution group expansion. Here’s what one looks like in message headers:
X-MS-Exchange-Organization-Network-Message-Id: 185a3445-695c-464a-d44c-08dcb7d88102
OR a different x-header that links to the same NMID value:
X-MS-Office365-Filtering-Correlation-Id: 185a3445-695c-464a-d44c-08dcb7d88102
Learn more about NMID.
Notes:
- When providing a recipient, use an Exchange Online (Microsoft 365) mailbox which received the message. If a message was sent to a group, trace the message to the individual recipient first, and then provide the recipient Network Message ID.
- The diagnostic also works for outbound messages and similarly requires the Network Message ID and the recipient address.
- In addition to threat policies applied to the message, this diagnostic can also be used to help you troubleshoot which inbound connector was used to receive the message. This information is available in extended message trace reports, but it is surfaced in the results for your quick reference, which is helpful if you’re using multiple connectors and inbound routing configurations.
Tip: Other self-help diagnostics are available for Exchange Online, Outlook and Microsoft Defender for Office 365. While these diagnostics can't make any changes to your tenant without your consent, they offer insights into known issues and provide instructions to fix those issues quickly.
Introducing: Threat Policy Checker PowerShell Script
Requirements: No parameters are required to perform general inclusion logic checks. Provide a recipient address for the policies scoped to a particular user.
Use the Threat Policy Checker Script to identify and resolve policy inconsistencies, and to ensure threat policies in your organization apply as intended. The script performs several checks to help you find inconsistencies in user membership and policy application without needing to provide a specific Network Message ID. If issues are found, the script provides guidance on how to resolve them. It can help with such questions as
- Are there confusing policies with conditions that lead to unexpected coverage or coverage gaps?
- Which threat policies apply to a recipient, or should have applied but did not? No actual detection or Network Message ID needed.
- Which actions would be taken on an email for each policy matched?
The script only runs in “Read” mode from Exchange Online and Microsoft Graph PowerShell. It does not modify any policies, and only provides actionable guidance for administrators for remediation.
Quick link: https://aka.ms/mdopolicycheck *
Parameters and Use Cases
MDOThreatPolicyChecker
Run the script without any parameters to review all threat protection policies and to find inconsistencies with user inclusion and/or exclusion conditions.
Script Output 1: 'No Logical inconsistencies found' message if the policies are configured correctly, and no further corrections are required.
Script Output 2: Inconsistencies found in the antispam policy named 'Custom antispam policy', and consequent recommendations shown -- illogical inclusions as both users and groups are specified. This policy will only apply to the users who are also members of the specified group.
-IncludeMDOPolicies
Add the parameter -IncludeMDOPolicies to view Microsoft Defender for Office 365 Safe Links and Safe Attachments policies:
Script Output 3: Parameters -EmailAddress and -IncludeMDOPoliciesEOP specified to validate Microsoft Defender for Office 365 Safe Attachments and Safe Links policies, on top of Exchange Online Protection policies.
-ShowDetailedPolicies
To see policy details, run the script with the -ShowDetailedPolicies parameter:
Script Output 4: Parameters -EmailAddress,-IncludeMDOPolicies, and -ShowDetailedPolicies list all EOP and MDO policies applied to a user and their full details.
* Please read the disclaimer when running the script. The scripts are not supported under any Microsoft standard support program or service. The sample scripts are provided AS IS without warranty of any kind. Please use GitHub to report issues to the developers.
We hope these tools help you evaluate and diagnose issues related to the order and precedence of email protection policies better. Do you have questions or feedback about Microsoft Defender for Office 365? Engage with the community and Microsoft experts in the Defender for Office 365 forum.
Important resources:
Email Threat Policy Diagnostic
Threat Policy Checker Script
Get started with Microsoft Defender for Office 365
Order and precedence of email protection
Preset security policies
Anti-spam message headers
Message trace in the new EAC in Exchange Online (NMID)
Self-help diagnostics for issues in Exchange Online and Outlook
Alex Hudish is a Senior Supportability Program Manager in the Customer Service & Support (CSS) Supportability Team focused on Security and Microsoft Defender for Office 365
Ross_Parkel is a Senior Technical Support Escalation Engineer in Customer Service & Support (CSS) focused on Security and Microsoft Defender for Office 365.
Mithun_Rathinam is a Senior Technical Support Escalation Engineer in Customer Service & Support (CSS) Beta Team focused on Security and Microsoft Defender for Office 365
Marc Nivens is a Senior Technical Support Embedded Escalation Engineer on the Microsoft Defender for Office 365 Team.
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