Email authentication fundamentals: SPF, DKIM, and DMARC

A great email only works if it reaches the inbox. As Gmail, Yahoo, and other providers enforce stricter sender requirements, deliverability has shifted from a creative challenge to a technical one — and authentication is now one of the biggest factors influencing whether your message gets seen.

This guide breaks down the three core authentication protocols — SPF, DKIM, and DMARC — and how they work together to protect your domain, strengthen your sender reputation, and improve inbox placement. You’ll also learn the essential setup steps and common pitfalls to avoid so your campaigns consistently reach the right audience.

Key takeaways

• Email authentication (SPF, DKIM, and DMARC) is now essential for reaching inboxes and protecting your brand from spoofing attacks.
• Start with monitoring-only DMARC policies, then gradually increase enforcement to avoid blocking legitimate emails during setup.
• Proper authentication directly improves deliverability rates, builds recipient trust, and increases email engagement and conversions.
• Test your authentication setup regularly using online validators and monitor DMARC reports to catch issues before they hurt campaigns.
• Automate the entire authentication process with smart software like monday campaigns, featuring step-by-step setup, real-time monitoring, and CRM integration.

What is email authentication?

Email authentication is a set of technical standards that verify your identity as an email sender. This means receiving servers can confirm you’re actually who you claim to be — not someone pretending to be your brand.

Think of it like showing ID at the airport. Just as TSA checks your license matches your boarding pass, email servers check that your messages come from authorized sources. Without this verification, anyone could send emails pretending to be your company. In the FBI’s most recent IC3 report, business email compromise resulted in over $2.77 billion in reported losses, making it one of the costliest cybercrime categories worldwide.

The 3 main authentication protocols work together to protect your emails:

1. SPF (Sender Policy Framework): Lists which servers can send email for your domain
2. DKIM (DomainKeys Identified Mail): Adds a digital signature proving your email hasn’t been tampered with
3. DMARC (Domain-based Message Authentication, Reporting & Conformance): Tells receiving servers what to do when authentication fails

SPF vs. DKIM vs. DMARC: Quick-look chart

SPF and DKIM authenticate your emails, while DMARC adds policy enforcement and visibility. Using all 3 protocols together is required to protect your brand, improve inbox placement, and keep up with modern sender requirements.

Gmail and Yahoo sender requirements (2024-25)

In February 2024, Gmail and Yahoo implemented strict sender requirements that fundamentally changed email deliverability. If you send more than 5,000 emails per day to Gmail or Yahoo addresses, you must now implement all 3 authentication protocols — no exceptions.

Here’s what these providers now require:

• SPF or DKIM authentication: At least one must pass (both recommended)
• DMARC policy: Minimum of p=none, though p=quarantine or p=reject provides better protection
• Valid forward and reverse DNS records: Your sending domains must have proper DNS configuration
• One-click unsubscribe: Marketing emails must include easy unsubscribe options
• Low spam complaint rates: Keep complaints below 0.3% (0.1% recommended)

These requirements aren’t suggestions — Gmail and Yahoo actively block emails that don’t comply. Even if you send fewer than 5,000 emails daily, following these standards improves deliverability across all providers. The email landscape has shifted from authentication being a best practice to being mandatory for inbox placement.

3 critical benefits of email authentication for marketers

Marketing leaders care about results — email open rates, conversions, and ROI. Email authentication directly impacts all 3 by protecting your sender reputation and ensuring messages reach inboxes. It also plays a crucial role in customer retention by keeping your communication channels secure.

1. Protect your brand from email spoofing

Email spoofing happens when criminals send fake emails that look like they’re from your company. They might send phishing links, fake invoices, or malware using your brand name.

Without authentication, there’s nothing stopping these attacks. Your customers receive fraudulent emails, lose trust in your brand, and may even suffer financial losses that ultimately lead to customer churn. Authentication creates a verification system that blocks these impersonation attempts before they reach anyone’s inbox.

2. Maximize email deliverability rates

Gmail, Outlook, and other email providers use authentication as a trust signal. When your emails pass authentication checks, providers know you’re legitimate and deliver your messages to the inbox.

Without proper authentication, even perfectly crafted marketing emails end up in spam folders, a common frustration given that 48% of senders report they struggle to stay out of spam. You waste campaign budgets reaching no one while competitors with authenticated emails land in prime inbox real estate.

3. Build recipient trust and engagement

Many email clients now show verified sender badges for authenticated emails. Recipients see these trust indicators and feel more confident opening your messages.

Higher confidence leads to higher engagement. When customers trust your emails, they open them, click your links, and boost your email conversion rates. With built-in authentication features, monday campaigns helps you build this trust automatically.

SPF authentication: Your first line of defense

SPF is a DNS record that lists every server authorized to send email for your domain. When someone receives an email from you, their server checks this list to verify the message came from an approved source.

How SPF validates sender identity

Here’s what happens when you send an email:

1. Your email leaves your server with your domain in the “from” address.
2. The receiving server sees your domain and looks up your SPF record.
3. If your sending server is on the approved list, the email passes.
4. If not, the email might be rejected or marked suspicious.

This entire process happens in milliseconds, protecting recipients from fake emails while ensuring your legitimate messages get through.

Creating an effective SPF record

An SPF record is a line of text in your DNS settings. A basic record looks like: v=spf1 include:_spf.google.com ~all

Let’s break down what each part means:

• v=spf1: Tells servers this is an SPF record
• include:_spf.google.com: Authorizes Google’s servers to send for you
• ~all: Marks unauthorized emails as suspicious (not rejected)

You’ll add different “include” statements for each email service you use — your marketing platform, CRM, support system, and so on.

SPF best practices for multiple senders

Most businesses use several email services. Your marketing team uses one platform, sales uses another, and support uses a third. Each needs authorization in your SPF record.

But here’s the catch: SPF has a 10 DNS lookup limit. Each “include” statement counts toward this limit. Go over 10, and your entire SPF record fails.

Smart organizations consolidate services where possible or use specialized SPF flattening services. With straightforward guidance on optimizing your SPF setup, monday campaigns simplifies this.

DKIM: Securing your email content

While SPF verifies who sent an email, DKIM verifies the email hasn’t been changed during delivery. It’s like a tamper-proof seal on your messages.

Understanding DKIM signatures

DKIM uses cryptography to create a unique signature for each email. Your email server creates this signature using a private key, then receiving servers verify it using your public key.

If someone tries to change your email — even one character — the signature breaks. The receiving server knows something’s wrong and can reject or quarantine the message.

Setting up DKIM for your domain

• Generate a key pair: Create public and private cryptographic keys
• Publish the public key: Add it to your DNS records
• Configure email signing: Set your email platform to sign outgoing messages

Most modern platforms handle this complexity for you. For example, monday campaigns automates the entire DKIM setup process, generating keys and providing simple DNS instructions.

DKIM key management guidelines

Strong security requires 2048-bit DKIM keys minimum. Shorter keys are easier to crack, putting your email security at risk.

Rotate your keys annually to maintain security. If a key gets compromised, rotation limits the damage window. Keep private keys secure — only authorized systems should have access.

DMARC: Unifying your email protection

DMARC is the conductor of your email authentication orchestra. It coordinates SPF and DKIM while adding an extra layer of verification called alignment.

How DMARC ties SPF and DKIM together

DMARC checks that the domain recipients see matches the domains used in authentication. This prevents sophisticated attacks where criminals pass SPF or DKIM but still impersonate your visible “from” address.

DMARC offers 2 alignment modes:

1. Relaxed alignment: Allows subdomains to match the main domain
2. Strict alignment: Requires exact domain matches

Most organizations start with relaxed alignment for flexibility, then tighten requirements as their email program matures.

Choosing the right DMARC policy

Begin with “none” to gather data without affecting delivery. Once you see consistent authentication success, move to “quarantine” and eventually “reject.”

DMARC reporting and monitoring

DMARC sends you reports showing:

• Who’s sending email using your domain
• Which messages pass or fail authentication
• Potential security threats or configuration issues

These reports reveal problems before they impact deliverability. Regular monitoring helps you maintain strong authentication and quickly spot unauthorized senders.

How to authenticate email: 5 essential steps

Ready to implement authentication? Follow these steps to protect your domain and improve deliverability.

Step 1: Audit your email sending sources

List every system that sends email for your domain. Include:

• Marketing platforms
• CRM systems
• Support platforms
• Internal servers
• Third-party integrations

You’ll likely find more sources than expected. Document each one’s purpose and sending volume for your SPF record.

Step 2: Implement SPF records

Create your SPF record starting with primary senders. Use the “~all” qualifier initially — it marks unauthorized emails as suspicious without blocking them.

Test your record with online validators. Watch for syntax errors and DNS lookup limits. Adjust as needed to include all legitimate senders.

Step 3: Configure DKIM signing

Enable DKIM in each email platform. Most generate keys automatically and provide DNS instructions.

Verify DKIM works by sending test emails and checking headers. Look for the DKIM-Signature field and use online validators to confirm proper signing.

Step 4: Deploy your DMARC policy

Start with a monitoring-only DMARC policy: v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com. This collects data without affecting delivery. Review reports to understand your authentication baseline before adding enforcement.

Step 5: Monitor authentication performance

Set up regular report reviews. Look for:

• Authentication failure patterns
• New unauthorized senders
• Configuration issues

Adjust your setup based on findings. Authentication isn’t set-and-forget — it requires ongoing attention as your email program evolves.

Email authentication testing and verification

Testing prevents surprises. Verify your authentication works correctly before launching major mass email campaigns.

Email authentication check platforms

Online testing platforms simulate how receiving servers process your emails. They check SPF syntax, DKIM signatures, and DMARC alignment in one comprehensive report.

These platforms often provide specific recommendations for fixing issues. Some offer ongoing monitoring to alert you when authentication problems arise.

How to verify SPF configuration

SPF testing involves 2 key checks:

• Syntax validation: Ensures your record follows proper formatting
• Authorization testing: Confirms all your senders pass authentication

Send test emails from each authorized source. Verify they pass SPF checks without errors or warnings.

Testing DKIM implementation

Check that DKIM signatures appear in your email headers. The signature should include your domain and selector information.

Use DKIM validators to verify signatures. Test across different email providers to ensure broad compatibility.

Validating DMARC alignment

DMARC testing confirms both authentication and alignment work correctly. Send test emails and verify:

• SPF or DKIM passes
• Domain alignment succeeds
• Policy actions work as expected

Test various scenarios to ensure comprehensive coverage. Your legitimate emails should pass while unauthorized attempts fail.

Common email authentication mistakes that hurt deliverability

Even experienced teams make these authentication errors. Learn from others’ mistakes to protect your deliverability.

1. Creating multiple SPF records

DNS allows only one SPF record per domain. Creating multiple records causes total authentication failure.

This happens when different teams manage email independently. The marketing team adds their record, IT adds another, and suddenly nothing works. Consolidate all senders into one comprehensive record.

2. Using weak DKIM keys

Keys shorter than 2048 bits don’t provide adequate security. Attackers can crack weak keys and send authenticated spam using your domain.

Always use 2048-bit keys minimum. If your platform defaults to shorter keys, manually configure stronger ones.

3. Setting DMARC too restrictive too soon

Jumping straight to “reject” policies can block legitimate emails. Important business communications might fail authentication due to minor configuration issues, so it’s best to start with monitoring, gradually increase enforcement, and use percentage rollouts for safety.

4. Neglecting subdomain authentication

Subdomains inherit parent domain DMARC policies. If you send from subdomains without proper authentication, those emails fail.

Configure SPF and DKIM for each sending subdomain. Consider separate DMARC policies if subdomain authentication needs differ from your main domain.

Simplify email authentication with monday campaigns

Managing authentication complexity distracts from what matters — creating campaigns that drive revenue. This complexity also disrupts email marketing productivity. monday campaigns handles technical details automatically while you focus on results.

Automated domain setup and verification

Guiding you through the authentication setup step-by-step, monday campaigns generates necessary records and provides direct DNS instructions.

Automatic verification confirms everything works correctly. No technical expertise required — just follow the prompts and start sending authenticated emails.

Real-time authentication monitoring

Built-in dashboards show authentication performance alongside campaign metrics. Spot issues immediately and understand how authentication impacts deliverability.

Automated alerts notify you of problems before they affect campaigns. Stay ahead of authentication issues without constant manual monitoring.

CRM-integrated authentication management

Native CRM with email marketing integration ensures consistent authentication across all customer touchpoints. Marketing emails that utilize email personalization, sales follow-ups, and support messages all benefit from proper authentication.

This unified approach strengthens your entire email program. Every message reinforces trust and protects your sender reputation, helping you reduce your email bounce rate.

Transform your email performance with proper authentication

Email authentication isn’t optional anymore — it’s essential for reaching inboxes and protecting your brand. Platforms that automate the heavy lifting have eliminated the technical complexity that once made authentication challenging.

Proper authentication delivers measurable business impact through improved deliverability, stronger engagement, and protected brand reputation. To further enhance your results, consider email segmentation to ensure each message reaches the right inbox. These benefits compound over time as your sender reputation strengthens.

Ready to implement authentication without the complexity? Let monday campaigns handle the technical details automatically, so you can focus on creating email sequences that convert.