Why SPF, DKIM, and DMARC Matter for Newsletter Deliverability

Your newsletter isn't reaching inboxes. And it's not because your subject lines are bad.

Email providers like Gmail, Outlook, and Yahoo are blocking or spam-filtering messages that lack proper authentication. If you're not using SPF, DKIM, and DMARC, you're losing subscribers before they even see your content.

This guide shows you how to set up all three protocols correctly and verify they're working. Use our email authentication checker at the end to confirm everything is configured properly.

What Are SPF, DKIM, and DMARC?

These three protocols verify that your emails are actually from you. They stop spammers from impersonating your domain and help your newsletters land in primary inboxes instead of spam folders.

SPF (Sender Policy Framework) tells email servers which IP addresses are allowed to send emails from your domain. It's a list of authorized senders.

DKIM (DomainKeys Identified Mail) adds a digital signature to your emails. It proves the message hasn't been tampered with during delivery.

DMARC (Domain-based Message Authentication, Reporting & Conformance) builds on SPF and DKIM. It tells email providers what to do if authentication fails and sends you reports on who's sending emails from your domain.

Think of it this way: SPF is your guest list, DKIM is your ID verification, and DMARC is your security policy.

Why This Matters More in 2025

Gmail and Yahoo started enforcing stricter email authentication requirements in 2024. By 2025, these rules are standard across major providers.

Without proper authentication:

• Your emails land in spam or promotions tabs
• Your sender reputation drops over time
• You lose subscribers who never see your content
• Domain spoofing damages your brand

With authentication set up:

• Higher inbox placement rates
• Better sender reputation
• Protection against phishing attacks using your domain
• Detailed reports on email delivery

Newsletter platforms like Beehiiv, Substack, and Kit handle some of this automatically. But if you're using a custom domain, you need to configure these records yourself.

How to Set Up SPF, DKIM, and DMARC

Setting Up SPF

SPF requires adding a TXT record to your domain's DNS settings.

Your newsletter platform provides the exact record. It usually looks like this:

v=spf1 include:sendgrid.net ~all

Understanding SPF syntax:

• v=spf1 identifies this as an SPF record
• include: adds authorized mail servers (each counts as a DNS lookup)
• ~all means soft fail (mark as suspicious but deliver)
• -all means hard fail (reject emails from unauthorized servers)

Steps:

1. Log into your domain registrar (Namecheap, GoDaddy, Cloudflare)
2. Find DNS settings or DNS management
3. Add a new TXT record for your root domain
4. Paste the SPF record from your email platform
5. Save and wait for propagation (typically 1 hour, up to 48 hours)

Critical SPF rules:

You can only have ONE SPF record per domain. Multiple SPF records will break authentication entirely.

SPF has a hard limit of 10 DNS lookups. Each include: statement counts as one lookup. If you exceed this limit, your SPF record fails and emails may be rejected.

Watch for the warning zone: If you're using 8-10 DNS lookups, you're approaching the limit. Audit your SPF record and remove any unused email services. If you need more than 10, consider SPF flattening services that reduce lookup counts.

Most newsletter creators use 3-5 services maximum (newsletter platform, Google Workspace, transactional email service). This keeps you well under the limit.

Setting Up DKIM

DKIM uses DNS records with cryptographic key pairs to sign your emails.

Your email platform generates these keys automatically. You just need to add them to DNS.

Understanding DKIM selectors:

A DKIM selector is part of the DNS record name that identifies which key to use. Different email services use different selectors, and one domain can have multiple DKIM records for different services.

Common selectors by platform:

• default._domainkey (most newsletter platforms)
• google._domainkey (Gmail/Google Workspace)
• s1._domainkey, s2._domainkey (SendGrid)
• mandrill._domainkey (Mailchimp/Mandrill)
• selector1._domainkey, selector2._domainkey (Microsoft 365)

When you validate DKIM, checkers automatically search for these common selectors. You don't need to know which one your platform uses.

Steps:

1. Get your DKIM record from your newsletter platform
2. Add a new TXT record in DNS (the name will include the selector, like default._domainkey.yourdomain.com)
3. Paste the DKIM value provided (this is your public key)
4. Save and verify in your platform's settings

Most platforms like Beehiiv and ConvertKit show a green checkmark when DKIM is configured correctly.

Best practice: Use 2048-bit key strength for DKIM. Most modern platforms default to this, but older setups might use 1024-bit keys. If your platform offers a key upgrade option, take it.

Setting Up DMARC

DMARC is the policy layer that tells email providers what to do with emails that fail SPF or DKIM checks.

Start with monitoring mode, then gradually increase strictness based on the reports you receive.

DMARC policy levels:

p=none (Monitoring mode) collects data without affecting delivery. Start here. You'll receive reports showing who's sending email from your domain and whether they're passing authentication. Use this for 2-4 weeks minimum.

p=quarantine (Cautious enforcement) sends suspicious emails to spam folders. Upgrade to this once you've confirmed legitimate emails are passing authentication.

p=reject (Strict enforcement) blocks suspicious emails entirely. Only use this when you're confident your authentication is solid and you've reviewed weeks of reports.

Basic DMARC record:

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

Understanding DMARC tags:

• v=DMARC1 identifies this as a DMARC record
• p=none sets your policy (none/quarantine/reject)
• rua= specifies where to send aggregate reports (daily summaries)
• ruf= specifies where to send forensic reports (detailed failure reports)

Steps:

1. Create a TXT record for _dmarc.yourdomain.com
2. Add the DMARC policy above
3. Monitor reports sent to your specified email
4. After 2-4 weeks of clean reports, upgrade to p=quarantine
5. After another 2-4 weeks, consider p=reject if appropriate

Important: You can only have ONE DMARC record per domain. Multiple DMARC records will cause authentication to fail.

Adding reporting addresses (rua= and ruf=) is optional but highly recommended. Without them, you won't know if legitimate emails are failing authentication or if someone's trying to spoof your domain.

What Happens If You Skip This

Email providers treat unauthenticated emails as suspicious. Your deliverability gradually declines as your sender reputation drops.

Competitors with proper authentication get inbox placement. You get spam folders. Subscribers assume you stopped sending. Your open rates decline week after week.

Without DMARC, scammers can spoof your domain for phishing attacks. Your brand gets associated with spam you didn't send. Subscribers report your domain, damaging your reputation further.

Setting this up takes under an hour in one sitting. The alternative is watching your newsletter performance deteriorate while you wonder why engagement is dropping.

Authentication isn't optional anymore. It's the baseline requirement for inbox delivery in 2025.

Conclusion

SPF, DKIM, and DMARC aren't optional in 2025. They're the baseline for serious newsletter senders.

Set them up in one sitting. Then verify everything is working correctly.

Use NewsletterStack's email authentication checker to validate all three protocols in seconds. It shows exactly what's configured, what needs fixing, and catches issues before they hurt your deliverability.

The checker searches common DKIM selectors automatically, validates your SPF lookup count, confirms your DMARC policy, and gives you clear pass/warning/fail status for each protocol.

Your subscribers can't read emails they never receive. Fix your authentication. Protect your deliverability.