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What is DMARC? A Guide to Email Authentication

Email is one of, if not the most important way in which businesses communicate with customers, suppliers and employees. Unfortunately, this has meant that it is now also one of the most common targets for cybercriminals.

Attackers will now frequently send fraudulent emails that appear to come from trusted organisations, making it easier to steal sensitive information, spread malware or trick recipients into making payments. This means that understanding DMARC is critical for cyber safety.

DMARC is an email authentication standard that helps businesses prevent this type of impersonation. By allowing organisations to prove that genuine emails are coming from authorised sources, it reduces the chances of spoofed messages reaching recipients. As well as strengthening email security, DMARC can improve trust in your brand and support better email deliverability.

Our experts have compiled this guide to explain what DMARC is, how it works, and why a carefully managed implementation is essential for any business, big or small.

What is DMARC and How Does It Work?

DMARC (Domain-based Message Authentication, Reporting and Conformance) is an email authentication standard that helps prevent criminals from sending emails that pretend to come from your business.

Rather than replacing existing email security measures, DMARC works alongside SPF (Sender Policy Framework) and DKIM (DomainKeys Identified Mail) to verify that emails sent using your domain are genuine and not being spoofed by a criminal element. When configured correctly, DMARC gives receiving mail servers clear instructions on how to handle suspicious emails, helping to protect your organisation from impersonation and phishing attacks.

Depending on your chosen policy, suspicious emails can be monitored, sent to a spam folder or rejected before they reach the recipient’s inbox. This gives organisations greater control over how their domain is used and helps receiving email providers distinguish between genuine messages and fraudulent ones.

When implemented and managed correctly, DMARC can provide a range of benefits for your organisation, including:

  • Preventing email spoofing and domain impersonation
  • Protecting your brand and business reputation
  • Improving email deliverability
  • Increasing trust with customers and suppliers
  • Gaining visibility of all systems sending email on your behalf
  • Meeting modern email security requirements from Microsoft, Google and other providers

Why DMARC Matters

Many businesses believe Microsoft 365 or Google Workspace automatically prevents someone from spoofing their email domain. While these platforms include a range of built-in security features, they don’t prevent attackers from sending emails that appear to come from your domain. Without a properly configured DMARC policy, cybercriminals can still impersonate your business and target customers, suppliers or employees with fraudulent messages.

Without DMARC enforcement:

  • Fraudsters can send emails pretending to be your business.
  • Customers may receive convincing fake invoices or payment requests.
  • Your domain reputation can suffer.
  • Genuine emails are more likely to be filtered as spam.
  • You have little visibility into who is sending email using your domain.

DMARC helps solve these problems by authenticating legitimate email and giving receiving mail systems confidence to reject fraudulent messages. When implemented correctly, it helps prevent domain impersonation, improves email deliverability and gives your organisation greater control over its email security.

What is a DMARC Policy?

p=none

Your domain is monitored, but fraudulent emails are still delivered. This provides visibility but very little protection.

p=quarantine

Suspicious emails are typically sent to the recipient’s spam or junk folder. This provides a higher level of protection but doesn’t stop every fraudulent message.

p=reject

Fraudulent emails that fail DMARC authentication are rejected before they reach the recipient’s mailbox.

This is the highest level of DMARC protection.

When your domain reaches p=reject, you’ve significantly reduced the risk of criminals successfully impersonating your business.

Why You Shouldn't Enable p=Reject Immediately

Although p=reject provides the highest level of DMARC protection, enabling it without the correct preparation can lead to consequences like legitimate business emails failing to deliver. Each of these services must be configured correctly with the appropriate SPF and DKIM authentication before a p=reject policy is enforced. Otherwise, emails from trusted systems could be rejected alongside fraudulent ones, which has the potential to disrupt business operations and customer communications.

Many organisations unknowingly have multiple systems sending email using their domain, including:

  • Microsoft 365
  • CRM systems
  • Marketing platforms
  • Finance software
  • Website contact forms
  • Booking systems
  • Printers and scanners
  • Third-party cloud applications
m365 platform

If these systems aren’t correctly authenticated before DMARC is enforced, genuine emails may be rejected. For these reasons, DMARC implementation should be introduced in stages.

Our managed service identifies every legitimate sender, configures the required authentication and carefully monitors your environment before gradually increasing your DMARC policy to full enforcement. Once the necessary authentication has been configured the system will continuously monitor your environment. When we’re confident that legitimate email is being authenticated successfully, we gradually increase your DMARC policy to full p=reject enforcement, helping you achieve maximum protection.

What is a DMARC Record?

A DMARC record is a DNS (Domain Name System) record that tells the mail servers receiving the messages how to handle the emails sent from your domain if they fail the authentication tests. It also specifies where DMARC reports should be sent, giving you visibility into email activity and potential spoofing attempts.

Once finally published, the record allows mail providers to follow your chosen DMARC policy and verify whether messages should be delivered, quarantined or rejected.

A basic DMARC record looks like this:

v=DMARC1; p=none; rua=mailto:dmarc@example.com;

This example identifies the record as DMARC, sets the policy to monitoring mode and specifies where aggregate reports should be sent.

What is a DMARC Report?

DMARC reports provide valuable insight into how your domain is being used and whether emails are passing authentication checks. They help identify legitimate email sources, detect potential spoofing attempts and highlight any systems that may need to be configured correctly.

Aggregate Reports

Aggregate (RUA) reports provide a summary of email authentication activity over a set period, usually every 24 hours. They show which servers are sending email using your domain, whether messages passed SPF and DKIM checks, and how receiving mail providers handled them.

Forensic Reports

Forensic (RUF) reports contain information about individual emails that fail DMARC authentication. They can help investigate specific spoofing attempts or authentication issues, although they’re not supported by every email provider and are less commonly used than aggregate reports.

Protect Against Email Spoofing With a Free DMARC Assessment

Implementing DMARC requires more than simply publishing a DNS record. Every organisation has a unique email environment, making it important to identify and authenticate all legitimate email sources before moving to full enforcement.

Birmingham Telecom’s managed DMARC email service takes care of the entire process, from configuring authentication records to monitoring reports and gradually strengthening your DMARC policy. With extensive IT expertise and years of experience supporting businesses, our team helps improve email security, reduce the risk of phishing and domain spoofing and protect your organisation’s reputation. We make implementing and managing DMARC straightforward, secure and hassle-free.

Picture of Stuart Hall | Commercial Manager

Stuart Hall | Commercial Manager

0121 716 8892
stuart@birminghamtelecom.co.uk

Birmingham Telecom Team

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