Email authentication best practices for 2025

Avoid these common email authentication mistakes to protect your domain and improve deliverability

A lot has changed in email authentication best practices since we first started helping our clients set up their websites. Email remains a cornerstone of business communication, but it’s also one of the primary targets for cybercriminals. Email providers are trying to counteract this with recent email authentication rules.

Now, stricter email authentication rules and heightened awareness of email-based threats means businesses have to adopt stronger email security measures.

This article will walk you through the fundamentals of email authentication — including SPF, DKIM, and DMARC. I’ll also explain what’s new and share email authentication best practices to keep your email communications secure and trusted.

Why email authentication matters

Email authentication protocols like SPF, DKIM, and DMARC are essential for verifying the legitimacy of emails sent from your domain. Without these measures, your business is vulnerable to several risks:

• Phishing and spoofing attacks: Cybercriminals can impersonate your domain to deceive recipients into divulging sensitive information. In 2022, over 500 million phishing attacks were reported globally, more than double the number from 2021.
• Reputational damage: If fraudulent emails appear to originate from your domain, it can erode customer trust and harm your brand’s reputation. In fact, 55 percent of phishing websites use targeted brand names to effectively capture sensitive information.
• Reduced email deliverability: Unauthenticated emails are more likely to be marked as spam, leading to legitimate communications not reaching their intended recipients. A security scan revealed that 9.3 percent of reported messages were malicious, with 38 percent containing just a URL and 36 percent having attachments.

The financial implications are significant. In 2022, phishing attacks resulted in over $52 million in losses in the U.S. alone.

Globally, business email compromise (BEC) scams accounted for $2.9 billion in losses in 2023, with an average loss of $174,000 per incident.

Now that providers are enforcing stricter email authentication rules, it’s important to implement robust email authentication protocols to safeguard your business against rising threats.

Overview of key email authentication protocols

In order to understand best practices, you need to understand how email authentication protocols — SPF, DKIM, and DMARC — work together. These three protocols ensure that emails sent from your domain are legitimate and trustworthy. Here’s how each protocol functions and why it’s essential:

SPF (Sender Policy Framework)

Think of SPF as a “guest list” for your email domain. It specifies which mail servers are allowed to send emails on your behalf. If an email is sent from a server not on the list, it fails the SPF check and may be flagged as suspicious or rejected outright.

How it works:

• When an email is sent, the receiving server checks the sender’s IP address against the SPF record stored in your domain’s DNS (Domain Name System).
• If the IP address matches one of the authorized servers in the SPF record, the email is considered legitimate.

Why SPF is important:

• It prevents spammers from forging your domain in their emails (a tactic known as spoofing).
• Ensures email servers trust your domain, improving email deliverability.

Steps to implement SPF:

1. Identify all servers and third-party services (like email marketing platforms) that send emails on behalf of your domain.
2. Add an SPF record to your DNS settings. This record is a simple text file listing the authorized mail servers.
3. Test your SPF record using online tools like MXToolbox to ensure it’s configured correctly.

DKIM (DomainKeys Identified Mail)

DKIM is like a “wax seal” on your email. It attaches a cryptographic signature to each outgoing email, verifying that the content hasn’t been altered during transit and that the email actually came from your domain.

How it works:

• Each outgoing email is signed with a private key unique to your domain.
• The recipient’s email server uses a public key, published in your DNS, to verify the signature.
• If the signature matches, the email passes the DKIM check.

Why DKIM is important:

• Protects against tampering during email transmission. For example, attackers can’t insert malicious links or attachments into an email without breaking the signature.
• Builds trust with email servers, further improving deliverability.

Steps to implement DKIM:

1. Generate a public-private key pair using your email provider’s tools.
2. Publish the public key in your DNS as a TXT record.
3. Enable DKIM signing in your email service provider (most major providers like Google Workspace or Microsoft 365 have built-in DKIM tools).

DMARC (Domain-based Message Authentication, Reporting & Conformance)

DMARC acts as the “traffic cop” for your email security. It ensures that SPF and DKIM are working together and gives you control over what happens to emails that fail authentication. Additionally, DMARC provides detailed reports about your email traffic.

How it works:

• DMARC checks whether incoming emails pass SPF and/or DKIM.
• Based on your DMARC policy, it determines how to handle unauthenticated emails (e.g., allow, quarantine, or reject them).
• It sends reports to you, detailing which emails passed or failed authentication and why.

Why DMARC is important:

• It helps protect your domain from being used in phishing attacks.
• Provides visibility into email activity, helping you identify unauthorized senders.

DMARC policies:

• None: No action is taken on unauthenticated emails, but reports are generated.
• Quarantine: Suspicious emails are marked as spam or moved to a quarantine folder.
• Reject: Unauthenticated emails are blocked outright, never reaching the recipient.

Steps to implement DMARC:

1. Publish a DMARC record in your DNS. This record specifies your policy and where to send reports.
2. Start with a “none” policy to monitor email traffic without affecting delivery.
3. Gradually move to stricter policies like “quarantine” or “reject” as you gain confidence in your configuration.

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How these protocols work together

• SPF ensures that only authorized servers can send emails from your domain.
• DKIM ensures that the content of the email hasn’t been altered and verifies its authenticity.
• DMARC ensures that SPF and DKIM work together and gives you control over how unauthenticated emails are handled.

By implementing all three protocols, you build a multi-layered defense against email-based threats, improving both security and deliverability.

What’s new in email authentication rules for 2024 and 2025

Email authentication has evolved significantly over the past few years, with new requirements introduced to combat spoofing, phishing, and other email-based threats. Here’s a breakdown of the key changes that came into effect in 2024 and how they’re shaping email security in 2025:

1. Mandatory DMARC enforcement

Starting February 1, 2024, email providers like Google and Yahoo began requiring bulk senders (those sending more than 5,000 emails daily) to implement DMARC with at least a “none” policy. This shift was designed to reduce email spoofing by encouraging more organizations to adopt DMARC, which works in tandem with SPF and DKIM to authenticate emails.

2. Subdomain authentication

One of the critical updates in 2024 was the enforcement of DMARC policies for subdomains. Previously, unauthenticated subdomains could bypass DMARC checks, creating vulnerabilities. Now, email providers require subdomains to adhere to the same DMARC policies as their parent domains, ensuring consistent authentication across all levels.

3. Advanced reporting requirements

As part of the new rules, businesses are encouraged — and in some cases required — to actively monitor and act on DMARC reports. These reports provide detailed insights into email traffic, authentication results, and potential threats, helping organizations identify misconfigurations and unauthorized use of their domains. This requirement has been carried into 2025 as a best practice for maintaining email security.

4. AI-Driven threat detection

In 2025, email providers are using artificial intelligence to enhance email security even more. AI tools analyze anomalies in SPF, DKIM, and DMARC configurations, flagging suspicious patterns and helping organizations respond to emerging threats more effectively. This trend represents a significant shift toward proactive threat mitigation using advanced technologies.

Why these changes matter

These updates reflect a growing commitment across the industry to strengthen email authentication and combat increasingly sophisticated email-based attacks. Whether your organization is adapting to the 2024 rules or preparing for AI-driven advancements in 2025, implementing robust email authentication protocols has become a critical aspect of protecting your domain, maintaining deliverability, and safeguarding your reputation.

Best practices for email authentication

Implementing email authentication isn’t just about setting up protocols—it’s about maintaining them to protect your domain and ensure optimal email deliverability. Here’s an expanded look at best practices to secure your email infrastructure:

1. Audit all sending domains

Your first step is to identify every domain and subdomain used to send emails, including those tied to:

• Marketing platforms (e.g., Mailchimp, HubSpot).
• Customer support systems (e.g., Zendesk, Salesforce).
• Transactional email services (e.g., Stripe, PayPal).

Attackers often exploit unprotected subdomains to send spoofed emails. Conducting a thorough audit ensures all domains and subdomains are properly authenticated.

Pro tip: Use DNS lookup tools to identify existing SPF, DKIM, and DMARC records for your domains.

2. Implement SPF, DKIM, and DMARC together

These three protocols form the foundation of email authentication, and using them in tandem provides the strongest protection:

• SPF validates the servers allowed to send emails for your domain.
• DKIM ensures email content remains unchanged in transit.
• DMARC aligns SPF and DKIM policies and provides reporting.

As mentioned above, each protocol addresses a specific aspect of email authentication. Together, they create a multi-layered defense that prevents unauthorized use of your domain.

Pro tip: Test your implementation using tools like MXToolbox to verify that SPF, DKIM, and DMARC are correctly configured.

3. Adopt a gradual DMARC enforcement policy

Start with a “none” policy to monitor email traffic and identify potential issues without affecting email deliverability. Once you’re confident in your setup:

• Move to a “quarantine” policy to mark suspicious emails as spam.
• Progress to a “reject” policy to block unauthorized emails entirely.

A gradual enforcement approach allows you to fine-tune your setup while minimizing disruptions to legitimate email delivery.

Pro tip: Monitor DMARC reports closely during the transition to stricter policies to catch and resolve any misconfigurations.

4. Monitor DMARC reports regularly

DMARC reports provide critical insights into your domain’s email activity, including:

• Authentication results for emails sent from your domain.
• Attempts by unauthorized senders to spoof your domain.

By analyzing DMARC reports, you can identify gaps in your setup, track down unauthorized senders, and optimize your email security.

Pro tip: Use tools like DMARCian or Postmark to aggregate and interpret DMARC reports for easier management.

5. Update records as services change

Every time you add or remove an email service provider, you need to update your DNS records, including SPF, DKIM, and DMARC. This includes:

• Adding new IP addresses or servers to your SPF record.
• Generating and publishing new DKIM keys.
• Ensuring DMARC policies cover changes in email flow.

Outdated records can cause legitimate emails to fail authentication, leading to delivery issues.

Pro tip: Set a regular schedule to review DNS records and make updates as needed.

6. Train your team

Your team plays a crucial role in maintaining email security. Training should cover:

• Recognizing phishing attempts and other email-based threats.
• Understanding the importance of SPF, DKIM, and DMARC.
• Reporting suspicious email activity to your IT or security team.

Even the most secure email systems can be compromised by human error. Educating your employees reduces the risk of phishing and other attacks.

Pro tip: Use phishing simulation tools to test and improve your team’s email security awareness.

Additional email authentication best practices

1. Partner with reliable email providers:
   Choose email providers that offer built-in support for SPF, DKIM, and DMARC and provide easy-to-use tools for managing authentication protocols.
2. Regularly test deliverability:
   Use email testing tools to ensure that your authenticated emails are reaching recipients’ inboxes.
3. Set up alerts for authentication failures:
   Many DMARC reporting tools allow you to set up alerts when emails fail authentication, enabling you to act quickly to resolve issues.

By following these email authentication best practices, you can build a secure email infrastructure, protect your domain from misuse, and ensure your emails consistently reach their intended audience. Let me know if you’d like further details or examples for any section!

Tools and resources for email authentication

• DMARCian – Analyze and monitor DMARC reports.
• MxToolbox – Test SPF, DKIM, and DMARC records.
• Postmark – Simplify email authentication with built-in tools.
• Google and Microsoft Documentation – Guides for setting up SPF, DKIM, and DMARC with major providers.

Common pitfalls to avoid

Even with robust protocols like SPF, DKIM, and DMARC in place, missteps in implementation or maintenance can undermine your email security. Here are some common pitfalls to watch out for and why they matter:

1. Ignoring authentication for subdomains

Subdomains are often overlooked during email authentication setup, leaving them vulnerable to exploitation by attackers. For example:

• If your primary domain has DMARC, SPF, and DKIM configured but your subdomains do not, attackers can spoof emails from unprotected subdomains (e.g., billing.yourdomain.com).

Many email providers now require subdomains to align with the authentication policies of the primary domain. Unauthenticated subdomains can be exploited for phishing or spoofing attacks.

How to avoid it:

• Ensure that all subdomains are covered under your SPF, DKIM, and DMARC policies.
• Use a wildcard DMARC record (e.g., *._domainkey.yourdomain.com) to protect all subdomains, or configure individual records for each.

2. Configuring overly restrictive SPF records

SPF records specify which servers are allowed to send emails for your domain. However, overly restrictive configurations can inadvertently block legitimate emails, such as:

• Emails sent from third-party services like CRMs, marketing platforms, or customer support tools that aren’t included in your SPF record.

When legitimate emails fail SPF authentication, they may be flagged as spam or rejected outright, harming deliverability and disrupting communication.

How to avoid it:

• Regularly audit your SPF record to include all authorized servers and services.
• Use SPF mechanisms like include: to add third-party providers to your SPF record.
• Test your SPF record with tools like MXToolbox to ensure it’s not overly restrictive.

3. Neglecting to monitor DMARC reports

DMARC reports provide valuable insights into your email authentication setup, highlighting:

• Unauthorized attempts to send emails from your domain.
• Configuration errors in your SPF, DKIM, or DMARC setup.

Failing to review these reports leaves you unaware of potential issues, such as:

• A spoofing attack targeting your domain.
• A misconfigured DNS record that causes legitimate emails to fail authentication.

Without monitoring DMARC reports, you can’t identify and address threats or misconfigurations, leaving your domain vulnerable.

How to avoid it:

• Use tools like DMARCian or Postmark to aggregate and visualize DMARC reports.
• Regularly review the reports to identify and resolve authentication failures or unauthorized activity.
• Set up alerts for unusual activity flagged in DMARC reports.

4. Forgetting to update DNS records when switching email services

Your DNS records must reflect changes in your email infrastructure. Common scenarios include:

• Migrating to a new email provider (e.g., switching from Microsoft 365 to Google Workspace).
• Adding or removing third-party services like marketing platforms or transactional email providers.

Outdated DNS records can result in failed email authentication, with legitimate emails being flagged as suspicious or rejected entirely.

How to avoid it:

• Maintain a clear inventory of all email-sending services and their DNS requirements.
• Review and update SPF, DKIM, and DMARC records whenever you add, remove, or change email services.
• Test your DNS records after updates to ensure correct configuration.

Additional pitfalls to watch out for

1. Not aligning SPF and DKIM with DMARC policies:
   • Ensure that both SPF and DKIM align with your DMARC policy to avoid authentication failures.
2. Using weak DKIM keys:
   • Always use at least a 2048-bit key for DKIM to prevent it from being compromised by attackers.
3. Leaving old DKIM keys active:
   • When rotating DKIM keys, deactivate old ones to prevent misuse by attackers.
4. Failing to gradually enforce DMARC policies:
   • Jumping straight to a “reject” policy without first using “none” or “quarantine” can disrupt email deliverability if your authentication setup isn’t fully functional.
5. Overlooking internal education:
   • A lack of training for your team can lead to human errors, such as misconfigured records or falling victim to phishing attempts.

By proactively addressing these pitfalls, you can maintain a robust and effective email authentication setup that secures your domain and ensures smooth email delivery. 

FAQ: Email authentication for 2025

1. Why is DMARC enforcement mandatory now?
   Email providers are prioritizing security and require DMARC enforcement to reduce phishing and spoofing. Without it, your emails may not be delivered.
2. Can I implement DMARC without SPF or DKIM?
   No, DMARC depends on SPF and/or DKIM to validate emails. Both need to be properly configured first.
3. How can I monitor DMARC reports?
   Use tools like DMARCian or MxToolbox to collect and analyze DMARC reports. These tools help identify unauthorized activity.
4. What happens if I miss updating my SPF record?
   If you fail to update your SPF record when changing email providers, legitimate emails may be flagged as unauthorized and rejected.
5. Do small businesses need to comply with these rules?
   Yes, email authentication is critical for businesses of all sizes. Cybercriminals often target smaller businesses, assuming they have weaker defenses.

Conclusion

With stricter email authentication rules in 2025, securing your domain is essential to protecting your reputation, preventing fraud, and ensuring email deliverability. By following these email authentication best practices, businesses can stay ahead of emerging threats and build trust with their audience.