How DMARC works in Microsoft 365 – email authentication policy
DMARC (Domain-based Message Authentication, Reporting & Conformance) in Microsoft 365 is a standard that combines SPF and DKIM to protect against email spoofing. DMARC defines how receiving servers should handle unverifiable messages and sends reports to administrators. This reduces the risk of phishing, spoofing and improves the deliverability of legitimate email.
Background and overview
DMARC is an important component of email security in Microsoft 365. By combining SPF and DKIM, DMARC creates a clear policy for how incoming email should be handled when authentication fails. Administrators also receive detailed reports that facilitate monitoring and action.
What is DMARC?
DMARC is a DNS-based policy that allows domain owners to specify how receiving servers should handle emails that do not pass SPF or DKIM verification.
How DMARC works
When a message is received, the receiving server checks the SPF and DKIM. If the message fails the verification, the server follows the DMARC policy, which may result in the message being delivered, quarantined or rejected.
Advantages of DMARC
DMARC reduces the risk of phishing and spoofing, protects the company’s domain and brand, and provides better insight into who is sending emails from the domain.
Reports and monitoring
DMARC generates reports that are sent to the domain owner or administrator. These reports show which messages passed or failed and help identify unauthorized senders.
Integration with SPF and DKIM
DMARC works best when SPF and DKIM are configured correctly. The policy ensures that only authenticated email reaches recipients and that erroneous messages are handled according to the specified policy.
Implementation in Microsoft 365
Administrators create a DMARC record in DNS, define the policy (no action, quarantine or rejection) and specify an email address for reports. This provides both protection and insight.
Common mistakes
Common mistakes are not configuring SPF and DKIM correctly before activating DMARC, applying too strict a policy right away or not reviewing the reports regularly.
Key points about DMARC in Microsoft 365
- Policy-based handling: Specifies how to handle emails that fail SPF/DKIM.
- Reports to administrators: Provides insight into incoming emails and unauthorized senders.
- Phishing protection: Reduces the risk of spoofing and email forgery.
- Integration with SPF and DKIM: Ensures that only authenticated emails reach recipients.
- Improved delivery reliability: legitimate messages are delivered without problems.
- Continuous monitoring: Administrators can analyze reports and update policies as needed.
Related questions
What is DMARC in Microsoft 365?
DMARC is a standard that combines SPF and DKIM to protect the domain against email spoofing and phishing.
How to implement DMARC?
The administrator creates a DMARC record in DNS, defines the policy (no action, quarantine or rejection) and specifies an email address for reports.
Why is DMARC needed together with SPF and DKIM?
To ensure that only authenticated emails reach recipients and that incorrect messages are handled correctly.
Can DMARC stop all phishing?
No, but it significantly reduces the risk when used in conjunction with proper SPF, DKIM and user training.
What happens if DMARC is not configured correctly?
Incorrect configuration can lead to legitimate messages being spammed or blocked by receiving servers.
