How to interpret Office 365 notifications for emails sent outside the organization?

Key findings

• Purpose: Office 365 external email notifications are security alerts, not direct DMARC failure messages.
• Source: These alerts originate from Microsoft's internal monitoring of your organization's email environment, flagging suspicious outbound activity.
• Triggers: Common triggers include a compromised user account, misconfigured sales or marketing automation tools, or unauthorized bulk sending.
• Severity: Microsoft classifies Suspicious email sending patterns detected as a medium-severity alert, serving as an early warning.

Key considerations

• Authentication issues: If third-party applications are sending emails on your behalf, ensure your SPF, DKIM, and DMARC records are correctly configured for all sending sources.
• Header review: Always examine email headers to determine the true origin of the message and verify if it legitimately came from a Microsoft IP address.
• Account security: Investigate any user accounts flagged for suspicious activity, as this could indicate a compromise or the installation of unwanted software. You can refer to Microsoft's official alert policies documentation for more details.
• DMARC data access: Leverage DMARC reporting, which Microsoft partners with Valimail for, to gain insights into email authentication failures and unauthorized sending across your domains.

Key opinions

• Not DMARC specific: Many marketers quickly point out that these notifications are generally not direct DMARC failure alerts but rather broader security warnings from Microsoft's internal systems.
• Spam indicators: Some marketers initially view these alerts as potential indicators of spam, questioning the legitimacy of the sending activity.
• Configuration concerns: Marketers often suspect that such notifications stem from misconfigured third-party email tools or applications used for sales or marketing automation.
• Spoofing or compromise: A common opinion is that the user's account might be compromised or their domain is being spoofed, leading to the suspicious sending patterns.

Key considerations

• Email flow rules: Marketers should check their Exchange Online mail flow rules, as these can be configured to add external email warnings or trigger alerts.
• Authentication setup: Ensuring correct SPF and DKIM authentication for all sending services, whether through Office 365 or external servers, is critical to avoid flags.
• Monitoring outbound activity: It's important to monitor for suspicious outbound email traffic, as it may indicate a compromised account or unwanted software, potentially leading to deliverability issues to Microsoft domains, as discussed in our guide on Outlook and Hotmail deliverability.
• Legitimacy verification: Marketers should always verify the legitimacy of any links or requests within these notifications, as some could be phishing attempts, even if they appear to come from Microsoft. More information on managing external email warnings can be found on Shoviv's blog.

Key opinions

• Focus on behavior: Experts emphasize that these alerts typically relate to suspicious sending behavior rather than just authentication failures, indicating potential compromises or misuse.
• Beyond DMARC: While DMARC is important for preventing spoofing, experts agree that these specific notifications are generally not direct consequences of DMARC check failures in the receiving system.
• Internal security: These are often internal security measures by Office 365 to warn administrators of potential issues with their own users or applications.
• Pre-emptive warnings: They serve as early warnings, alerting about risks of a user being restricted from sending, before it becomes a widespread deliverability problem.

Key considerations

• Compromised accounts: A key concern is that the user's account might be compromised, which necessitates immediate investigation and remediation steps.
• Authentication setup: Experts reiterate that if third-party services are sending emails, proper authentication records (SPF, DKIM, DMARC) must be in place and aligned with the sending domains.
• Header analysis: Analyzing email headers remains crucial to understand the mail flow and identify any discrepancies or unauthorized sending paths. This can reveal why your emails might be going to spam.
• Proactive monitoring: Using tools for DMARC reporting and analytics can provide deep insights into sending practices and quickly identify suspicious activity, reducing the chances of future alerts.

Key findings

• Alert policies: Microsoft 365 uses alert policies to generate notifications for various security and compliance events, including suspicious email activity.
• Suspicious sending patterns: An alert like Suspicious email sending patterns detected is a standard, predefined policy.
• Severity: This specific alert typically has a Medium severity setting by default.
• Purpose of alert: It serves as an early warning to indicate that a user account might be compromised and is at risk of being restricted from sending email.

Key considerations

• Anomaly vs. compromise: While alerts can sometimes be anomalies, the documentation strongly recommends checking the user account for compromise to rule out security breaches.
• Custom alerts: Administrators can configure custom alert policies to monitor specific outbound email patterns or content.
• Mail flow rules: Microsoft documentation also details how to set up mail flow rules (transport rules) in Exchange Online to add warnings to emails originating from outside the organization, enhancing user awareness of external communications. This helps in troubleshooting Outlook email deliverability.
• Understanding Organization context: The term outside the organization refers to email activity that originates from a domain or sender not part of the configured Microsoft 365 tenant.