SPF, DKIM and DMARC Explained for Founders

Quick answer: SPF, DKIM, and DMARC are DNS records that verify your identity as an email sender. SPF lists authorized servers, DKIM provides a digital signature to prevent tampering, and DMARC tells receivers how to handle emails that fail these checks. Proper setup is essential in 2026 to prevent spam folders and domain spoofing.

By Gabriel CA · Kraftwire Software

· 6 min read

Email authentication is no longer a technical choice for founders · it is a business requirement. Without these three pillars, your transactional emails land in spam, your marketing campaigns fail, and your domain becomes a target for spoofing.

For founders building with vibe-coding tools like Lovable or Bolt.new, email setup is often an afterthought. However, in SimplyScan's scans of 177 AI-built apps, 33% had at least one high or critical severity issue, and many of these relate to how the application interacts with external services like DNS and email providers. If you do not own your email identity, someone else can use it.

Why Do You Need SPF DKIM and DMARC Explained?

Email was designed in an era when the internet was a small, trusted community. The original protocols did not include a way to verify that the sender listed in the "From" field was actually the person who sent the message. This flaw created a multi-billion dollar industry for phishing and spoofing.

SPF, DKIM, and DMARC are the three layers of defense that fix this. Think of them as a passport system:

  • SPF is the authorized list of departure airports (which servers can send mail).
  • DKIM is the digital seal on the envelope (proving the content hasn't been tampered with).
  • DMARC is the instruction manual for the receiving airport (what to do if the passport or seal is missing).

How Does SPF Work to Prevent Spoofing?

SPF (Sender Policy Framework) is a simple TXT record in your DNS. It lists the IP addresses or services (like Postmark, SendGrid, or Resend) that are allowed to send email on behalf of your domain.

When an email arrives, the recipient's server looks at the "Return-Path" address, checks the DNS of that domain, and sees if the sender's IP is on the list. If it is not, the email may be flagged as suspicious.

The 10 Lookup Limit

A common mistake for founders is adding too many services to their SPF record. If you use include:google.com, include:sendgrid.net, and several others, you might exceed this limit. As noted by industry experts in early 2026, tracking lookup counts becomes a critical operational task for maintaining deliverability. If you exceed 10, the SPF check fails entirely, even for authorized senders.

What Is DKIM and Why Is It Better Than SPF?

DKIM (DomainKeys Identified Mail) provides a cryptographic signature for your emails. While SPF only validates the "envelope" (the server sending the mail), DKIM validates the content.

When you set up DKIM, your email provider generates a private key to sign every outgoing email and gives you a public key to publish in your DNS. The receiving server uses the public key to verify the signature. If the email was modified in transit · for example, if a malicious actor tried to swap a link in your password reset email · the signature would break, and the email would fail the check.

For founders using vibe-coding tools, ensuring your backend service (like Supabase or Xano) is correctly configured with DKIM is vital for API security best practices.

Why Is DMARC the Most Important Record?

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is the policy layer. It tells the world what to do when an email fails SPF or DKIM checks. Without DMARC, a failure might just result in a "neutral" result, and the email might still be delivered.

DMARC allows you to set one of three policies:

  • p=none: Monitor only. No action is taken against failing emails.
  • p=quarantine: Send failing emails to the spam folder.
  • p=reject: Block failing emails entirely.

According to recent regulatory shifts in 2026, DMARC is now viewed as a cross-sector cybersecurity performance goal by agencies like CISA. It is no longer just a "best practice" but a requirement for maintaining a professional domain reputation.

How Do You Set Up These Records for a New App?

If you are deploying an app via Vercel or Netlify, you likely use a third-party email provider. Here is the standard workflow:

  • Choose an Email Provider: Services like Resend or Postmark are popular for AI-built apps.
  • Add SPF: Add a TXT record to your DNS. It usually looks like v=spf1 include:amazonses.com ~all.
  • Add DKIM: Your provider will give you two or three CNAME records. Add these to your DNS.
  • Add DMARC: Start with a "none" policy to ensure your setup is correct: v=DMARC1; p=none; rua=mailto:admin@yourdomain.com.
  • Monitor Reports: Check the XML reports sent to your "rua" address to see if any legitimate mail is failing.
  • Enforce: Once you are confident, move to p=quarantine and eventually p=reject.

What Are the Risks of Ignoring Email Security?

Ignoring these records leads to two primary failures: deliverability collapse and brand impersonation.

Deliverability Collapse

If you send a "Welcome" email from a new Bubble or FlutterFlow app without these records, it will likely never reach the user's inbox. This breaks your onboarding flow and kills your conversion rate.

Brand Impersonation

Without a p=reject DMARC policy, anyone can send an email that appears to come from support@yourstartup.com. They can target your users with fake "billing update" requests or "security alerts" to steal credentials. This is especially dangerous if your app handles sensitive data, as seen in our Supabase security checklist.

How Can You Audit Your Domain Health?

Manually checking DNS records is tedious and prone to error. You might have a valid SPF record but a broken DKIM selector, or a DMARC policy that is too weak to protect you.

SimplyScan provides a comprehensive email security tool as part of its free site health scan. In about 30 seconds, the scanner checks your SPF, DKIM, and DMARC records alongside other critical factors like DNS security and SSL health.

In SimplyScan's scans of 177 AI-built apps, while the average security score was 86 out of 100, 20% of apps still flagged medium-severity security issues, often involving misconfigured headers or records. Using a security scanner helps you catch these gaps before they impact your users.

Summary Checklist for Founders

  • Check your SPF record for the 10-lookup limit.
  • Ensure DKIM is enabled for every service that sends mail (Helpdesk, CRM, App).
  • Set a DMARC policy, even if it is just p=none for now.
  • Use a tool like SimplyScan to verify your domain health.

By taking 15 minutes to configure these records correctly, you protect your brand's reputation and ensure that your application's communications remain reliable as you scale. For more help securing your stack, check out our vibe-coding security checklist.

SimplyScan offers a free scan that grades 8 dimensions in one pass · security, speed, SEO, AI visibility, accessibility, GDPR signals, domain health, and email security · in ~30 seconds with no signup. It is the fastest way for founders to ensure their AI-built apps are production-ready. For teams needing ongoing peace of mind, Pro Monitoring at $24/month provides uptime monitoring and scheduled rescans with Slack and GitHub integrations.

Frequently asked questions

What is SPF and how does it work?

SPF (Sender Policy Framework) is a DNS TXT record that specifies which mail servers are authorized to send email on behalf of your domain. It prevents unauthorized servers from sending mail that appears to come from you, though it has a 10-lookup limit that founders must manage carefully to avoid deliverability failures.

Why is DKIM important for email security?

DKIM (DomainKeys Identified Mail) adds a cryptographic signature to your emails. The receiving server uses a public key in your DNS to verify that the email was actually sent by your domain and that the content has not been altered in transit. It is more robust than SPF because it stays with the email even if it is forwarded.

What does a DMARC policy actually do?

DMARC (Domain-based Message Authentication, Reporting, and Conformance) is a policy that tells receiving servers what to do if an email fails SPF or DKIM checks. You can tell them to do nothing (none), put it in spam (quarantine), or block it entirely (reject). It also provides reporting so you can see who is sending mail as your domain.

What happens if I don't set up email authentication?

In 2026, major providers like Google and Yahoo require these records for bulk senders. Without them, your emails are highly likely to be marked as spam or blocked entirely. Furthermore, without DMARC, attackers can easily spoof your domain to send phishing emails to your customers, damaging your brand reputation and trust.

How do I check if my SPF DKIM and DMARC are set up correctly?

Start by adding SPF and DKIM records provided by your email service (like Resend or Postmark). Then, add a DMARC record with p=none to monitor your traffic. Use a tool like SimplyScan to verify the records are live and valid. Once your reports show that legitimate mail is passing, update your DMARC policy to p=quarantine or p=reject.

What is the SPF 10-lookup limit and how do I fix it?

The SPF 10-lookup limit is a restriction where the receiving server will only perform 10 DNS lookups to resolve an SPF record. If your record includes too many external services (like Google, Zendesk, and HubSpot), it may fail. You can fix this by removing unused services or using SPF flattening tools.

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  • DNS Records Explained: A, CNAME, MX, TXT, NS and CAA for App Builders · DNS records tell the internet where your app loads, where your email lands, and who may issue certificates for your domain. A and AAAA map names to addresses, CNAME aliases them, MX routes mail, TXT carries SPF, DKIM and DMARC, NS delegates control, and CAA restricts certificate issuance · audit all six regularly.

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