What is DMARC and how can you set it up?

DMARC – short for Domain-based Message Au­then­tic­a­tion Reporting and Con­form­ance – helps receivers dis­tin­guish fraud­u­lent emails from genuine ones. It’s es­pe­cially useful for domain owners because it keeps domains off black­lists and reduces the risk of messages being rejected or treated as spam.

What is DMARC?

DMARC stands for Domain-based Message Au­then­tic­a­tion, Reporting and Con­form­ance. It builds on existing au­then­tic­a­tion methods like SPF and DKIM by giving receiving mail servers clear in­struc­tions for handling messages that fail those checks.

How does DMARC work?

• Domain owners publish a DMARC policy as a DNS TXT record.
• Receiving servers evaluate incoming mail using SPF and/or DKIM.
• If au­then­tic­a­tion fails, the receiving server enforces the policy defined in the DMARC record.
• Reports can be sent to the domain owners to help them spot potential attacks and take action.

Overview of DMARC policies

How DMARC reporting works

An essential component of DMARC is its feedback system. This system informs domain owners about possible misuse or spoofing attempts:

• Aggregate reports (rua): Daily summaries of all checked emails, typically provided in XML format. These reports provide in­form­a­tion on the volume, source and results of au­then­tic­a­tion checks.
• Forensic Reports (ruf): Detailed in­di­vidu­al reports on failed checks that may contain specific header fields and content sections from the sus­pi­cious message.

Bear in mind that these reports can include sensitive data such as email addresses, sender details and technical in­form­a­tion. When setting up your reporting, make sure you comply with any reg­u­la­tions related to data pro­tec­tion that may apply.

What does a DMARC record contain?

A DMARC record is stored as a TXT record in a domain’s DNS. It contains several para­met­ers that together define how incoming messages are handled.

DMARC tags and their meaning

Example DMARC Record

_dmarc.example.co.uk. IN TXT "v=DMARC1; p=quarantine; rua=mailto:dmarc-reports@example.co.uk; ruf=mailto:dmarc-forensic@example.co.uk; pct=100; adkim=s; aspf=s"

How to create a DMARC record

Before you can create a DMARC record, SPF and DKIM records must already exist for your domain. DMARC will only work properly once this found­a­tion is in place.

Step 1: Generate a DMARC record

Use an online tool, such as the DMARC Record Generator by EasyDMARC. Enter your domain along with the required para­met­ers, including the policy type and the addresses for DMARC reports.

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Step 2: Create the TXT record in DNS

Next, log in to your domain provider account and open the DNS settings. Create a TXT record with the following values to configure the DMARC record for your domain:

• Subdomain: _dmarc.yourdomain.co.uk
• Type: TXT
• Value: the DMARC record created by the generator

Example:

_dmarc.yourdomain.co.uk. IN TXT "v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.co.uk"

Step 3: Introduce the policy gradually

1. Start with p=none

• Mon­it­or­ing only. Emails are delivered normally.
• Analyse the DMARC reports to check whether all le­git­im­ate servers are correctly au­then­tic­ated.

2. Switch to p=quarantine

• Sus­pi­cious emails are moved to spam or quar­ant­ine.
• The risk of domain abuse decreases sig­ni­fic­antly.

3. Finish with p=reject

• Un­au­thentic­ated emails are blocked and not delivered.
• This is the re­com­men­ded final stage for domains with fully es­tab­lished SPF and DKIM records.

It’s best to begin with the policy set to none and monitor the reports for a period to ensure results are as expected.

Step 4: Set up reporting address

Create a dedicated address, such as dmarc-reports@yourdomain.co.uk and use it ex­clus­ively for DMARC reports. This keeps main inboxes from being over­loaded with XML files. You can also add a second mailbox for forensic reports, such as dmarc-forensic@yourdomain.co.uk.

Keep the following points in mind:

• Separate reports: Only use these mailboxes for DMARC data so they stay organised and are easy to monitor.
• Allow external senders in DNS: To receive reports from external mail servers, your domain must ex­pli­citly permit this in the DNS. Without that au­thor­isa­tion, no reports will arrive even if your DMARC record is correct.
• Respect data pro­tec­tion: DMARC reports include sensitive details such as IP and email addresses. Always handle them in line with your company’s data pro­tec­tion policies and, where ap­plic­able, the GDPR.

Step 5: Monitor results

Use dedicated tools to analyse incoming reports and identify misuse at an early stage. Services such as Google Post­mas­ter Tools or Microsoft SNDS (Smart Network Data Services) help you visualise how your domain is being used, or misused, and make it easier to fine-tune your DMARC policy.

Step 6: Verify your DMARC record

Depending on your name server, pub­lish­ing the record can take anywhere between a few minutes and several hours. To confirm that the entry is active and correctly con­figured, use a DMARC check tool, such as the DMARC Record Lookup Tool by EasyDMARC.

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