Common DMARC Issues In Office 365
And How To Fix Them

Domain-based Message Authentication, Reporting, and Conformance (DMARC) is an essential protocol for email authentication that plays a crucial role in safeguarding against spoofing, phishing, and fraudulent emails. When set up properly, DMARC boosts email security by guaranteeing that only authentic emails from your domain are delivered to recipients' inboxes.

Nevertheless, many organizations utilizing Microsoft Office 365 face several DMARC-related challenges stemming from configuration errors or incompatibilities with Microsoft's email system. This guide aims to identify prevalent DMARC issues within Office 365 and offer effective solutions to resolve them.

Common DMARC Issues and Solutions

1. DMARC Policy Not Enforced Properly

A common challenge with DMARC is that companies establish a policy but do not implement it effectively. Often, administrators opt for a "p=none" setting by default, which merely observes email interactions without providing any security measures.

To address the issue, gradually tighten the DMARC policy, moving from "p=none" to "p=quarantine" and finally to "p=reject" as you gain confidence in your authentication methods.

Additionally, make use of DMARC reports to monitor for any suspicious email behavior before implementing stricter policies.

2. SPF and DKIM Misconfiguration

DMARC depends on the Sender Policy Framework (SPF) and DomainKeys Identified Mail (DKIM) for its authentication process. If there are any errors in the configuration of these protocols, it can lead to a failure in DMARC verification.

To resolve this issue:

Make sure that your SPF record encompasses all permitted sending sources. For Office 365, a correctly formatted SPF record should appear as follows:

v=spf1 include:spf.protection.outlook.com -all

Activate DKIM signing within Office 365 via the Microsoft Defender portal:

Go to Microsoft Defender > Email authentication settings.

Turn on DKIM for your domain and copy the required CNAME records into your DNS settings.

3. Office 365 Forwarding and External Email Handling

Emails that are forwarded can encounter DMARC verification issues due to SPF failures when the forwarding server isn’t included in the original sender's SPF record.

The recommended approach is to encourage the adoption of DKIM, as it remains intact when emails are forwarded. If issues with forwarding persist, consider adopting a more flexible DMARC policy by configuring "sp=none" for subdomains. Additionally, when using third-party email services, make sure they adhere to DMARC regulations.

4. Legitimate Emails Failing DMARC

Genuine emails can be blocked or placed in quarantine because of DMARC issues stemming from authentication discrepancies.

Steps to Resolve the Issue:

Confirm that all external email senders are included in your SPF record.

Check that DKIM signing is activated for every domain.

Utilize DMARC aggregate reports to pinpoint sources of failed emails and adjust your authentication records as needed.

5. Misinterpretation of DMARC Reports

DMARC produces reports that provide insights into an organization's email authentication status. Nonetheless, making sense of these reports can be difficult, which may result in misguided policy changes.

Solutions:

Utilize DMARC reporting solutions like DMARC Analyzer, Agari, or Microsoft Defender to make report interpretation easier.

Consistently examine reports to identify any unauthorized email behavior and enhance your authentication strategies.

6. Conflicts with Third-Party Email Services

Many organizations rely on external services, such as marketing tools and customer support software, to handle their email communications. If these services are not set up correctly, DMARC can block their emails.