How to Stop Email Spoofing Attacks and Phishing Attacks with DMARC

Email is one of the most important tools for business communication, but it's also one of the easiest to exploit. Attackers use spoofing and phishing campaigns to impersonate trusted senders, steal credentials, and distribute malware.

Spoofed emails can appear indistinguishable from genuine ones, leading to financial loss and reputational damage. The good news? You can stop these attacks at the source with DMARC.

What Is Email Spoofing?

Email spoofing is the act of forging an email’s “From” address to make it look like it was sent from someone else, often a legitimate business or colleague.

Attackers do this to:

• Trick users into sharing sensitive data (credentials, payment info, etc.)
• Deliver malicious attachments or links
• Conduct business email compromise (BEC) scams

Without proper authentication, email servers have no way of knowing whether the “From” address is real or forged.

What Is DMARC?

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is an open standard that prevents unauthorized senders from using your domain.

It builds on two existing authentication methods:

• SPF (Sender Policy Framework) - Verifies that the sender’s IP is allowed to send on behalf of your domain.
• DKIM (DomainKeys Identified Mail) - Uses cryptographic signatures to confirm message integrity and authenticity.

DMARC acts as the policy layer on top of these mechanisms. It tells receiving servers what to do if an email fails SPF or DKIM checks, and provides reports so you can see who’s sending mail using your domain.

How DMARC Works (Step by Step)

1. SPF and DKIM Validation
   When an email arrives, the recipient’s mail server checks whether the sender’s IP is listed in the domain’s SPF record and whether the DKIM signature matches a valid key published in DNS.
   
   
2. Alignment Check
   DMARC verifies “alignment,” meaning the domain in the email’s From: header matches (or aligns with) the domain authenticated by SPF or DKIM. This is what stops attackers from passing SPF or DKIM using unrelated domains.
   
   
3. Policy Application
   Based on your DMARC policy (p=none, p=quarantine, or p=reject), the receiving server decides whether to deliver, spam-folder, or reject the email.
   
   
4. Reporting and Visibility
   DMARC provides two types of reports:

• 1. RUA (Aggregate reports): Summarized daily reports showing which IPs are sending mail for your domain.
  2. RUF (Forensic reports): Detailed copies of individual failed messages for deeper investigation.

These reports are sent to the addresses you specify in your DMARC record and can be analyzed with visualization tools.

Why SPF and DKIM Aren’t Enough

SPF and DKIM are essential, but by themselves they don’t protect against direct domain spoofing.

For example:

• SPF checks only the envelope sender (Return-Path:), not the visible From: header.
• DKIM can authenticate the message content, but attackers can still use a different domain in the “From” field.

DMARC closes this gap by enforcing domain alignment, ensuring that the domain your customers see is the same one authenticated by SPF or DKIM.

How to Implement DMARC (A Step-by-Step Guide)

Implementing DMARC doesn’t require new hardware or software, just DNS access, planning, and a few weeks of observation. Below is a concrete, reliable roadmap.

Step 1: Inventory All Legitimate Email Sources

Before publishing anything, make a complete list of every service that sends mail using your domain. This typically includes:

• Your primary mail server (e.g., Microsoft 365, Google Workspace)
• Transactional senders (e.g., SendGrid, Amazon SES)
• Marketing platforms (e.g., HubSpot, Mailchimp)
• Helpdesk/ticketing systems (e.g., Zendesk)
• Billing or ERP tools that send invoices

Tip: Search your logs or DMARC reports for any “From” addresses under your domain to catch hidden or forgotten sources.

Step 2: Configure SPF and DKIM for Each Sender

DMARC relies on SPF and DKIM being properly configured.

For SPF:

• Google Workspace: include:_spf.google.com
  
• Microsoft 365: include:spf.protection.outlook.com
  
• Mailchimp: include:servers.mcsv.net

Combine them into one SPF record (if possible):

v=spf1 include:_spf.google.com include:servers.mcsv.net -all

For DKIM:

Publish the DKIM public key in DNS — typically at a subdomain like:

google._domainkey.yourdomain.com

Step 3: Publish a Basic DMARC Record

Once SPF and DKIM are working, add your initial DMARC record:

v=DMARC1; p=none; rua=mailto:dmarc-reports@yourdomain.com; ruf=mailto:dmarc-forensic@yourdomain.com; fo=1

This record:

• Activates DMARC in “monitor” mode (no enforcement yet)
• Sends aggregate (RUA) and forensic (RUF) reports to the listed addresses
• Uses fo=1 to request forensic reports for any failure

Publish this as a TXT record at:
_dmarc.yourdomain.com

Step 4: Monitor and Analyze Reports

Over the next few weeks, you’ll start receiving XML-based DMARC reports from mail servers around the world.

They include:

• Source IP addresses
• Sending domains
• Pass/fail results for SPF and DKIM
• Message counts per sender

You can process these reports manually or (more realistically) through a DMARC reporting tool that visualizes senders, volumes, and authentication results.

Goal: Identify all legitimate sources, correct any misconfigurations, and flag unknown senders (likely spoofers or misconfigured vendors).

Step 5: Tighten Your Policy Gradually

Once you’re confident all legitimate email flows are authenticated and aligned, begin enforcing your policy in stages:

Move to Quarantine

v=DMARC1; p=quarantine; pct=25; rua=mailto:dmarc-reports@yourdomain.com

• Quarantines 25% of failed messages (sent to spam)
• Lets you monitor the impact safely
• Gradually raise pct to 100% once stable

Move to Reject

v=DMARC1; p=reject; rua=mailto:dmarc-reports@yourdomain.com

• Fully blocks unauthenticated email
• Provides maximum protection against spoofing

Step 6: Maintain and Expand

DMARC isn’t “set and forget.” You need to:

• Review reports regularly to detect new unauthorized sources.
• Add new vendors to SPF/DKIM as your infrastructure evolves.
• Apply DMARC to subdomains if they also send mail (admissions.yourdomain.com, news.yourdomain.com, etc.).
• Consider adding a BIMI record to display your brand logo in inboxes — available only with enforced DMARC.

Here's an Example DMARC Implementation Timeline

Troubleshooting Tips

• Problem: Legitimate emails going to spam after enforcement
  → Check DKIM alignment and SPF includes for that sender.
• Problem: SPF record too long (>255 characters)
  → Use subdomains or third-party flattening tools.
• Problem: Missing DMARC reports
  → Verify your rua mailbox can receive XML attachments.

DMARC Protects Against Phishing

Phishing relies on trust. Attackers impersonate known brands or colleagues to trick victims into clicking malicious links or sharing information.

DMARC undermines this trust-based attack by preventing unauthenticated emails from ever reaching the inbox. If a cybercriminal tries to send mail from “support@yourdomain.com” but isn’t authorized, that email is rejected before it’s seen.

For customers, partners, and employees, this creates a visible line between legitimate communication and fraud.

Beyond DMARC: Strengthening Your Email Security Posture

DMARC is a major step, but not a complete solution. To build comprehensive protection:

• Use BIMI (Brand Indicators for Message Identification) to display verified brand logos in inboxes.
• Combine DMARC with DNSSEC for tamper-proof DNS authentication.
• Educate staff about social engineering and phishing awareness.

Together, these create a layered defense that blends technical and human security controls.

How DMARCeye Simplifies DMARC Implementation and Monitoring

Implementing DMARC manually is possible, but interpreting the data, keeping records aligned across multiple services, and maintaining enforcement as your infrastructure evolves can quickly become complex.

DMARCeye is an AI-powered visibility and reporting platform designed to make DMARC management simple, transparent, and actionable. It transforms raw XML reports into clear, human-readable dashboards so you can:

• Instantly see which senders are authorized and which aren’t
• Track your SPF, DKIM, and DMARC alignment status across all domains
• Identify and block spoofing attempts in real time
• Confidently move from monitoring to full enforcement
• Maintain deliverability while securing your brand’s reputation

With guided setup, automated analysis, and ongoing monitoring, DMARCeye gives organizations of all sizes the control and clarity needed to protect their domain from email spoofing and phishing threats, without deep DNS expertise.

Get a free trial of DMARCeye today and start protecting your email domain.