Sender Policy Framework (SPF) is crucial for email authentication, helping prevent spoofing and phishing. However, SPF has a limit on the number of DNS lookups (10), leading some administrators to use SPF flattening—a process that replaces domain-based SPF mechanisms (include) with direct IP addresses to reduce lookups. While this may seem beneficial, many email services advise against SPF flattening due to its risks.

This guide explains why SPF flattening is discouraged, the potential issues it causes, and better alternatives for managing SPF records efficiently.

SPF flattening is a technique where all indirect include mechanisms in an SPF record are replaced with their corresponding IP addresses. This reduces the total number of DNS lookups but introduces several challenges.

Example Before SPF Flattening:

Example After SPF Flattening:

Here, instead of using domain-based includes, the SPF record lists specific IP addresses.

Email service providers frequently change their sending IP addresses. Flattening your SPF record means listing static IPs, which may become outdated if the provider updates their infrastructure. This can lead to email delivery failures.

Flattening is often done to stay under the 10 DNS lookup limit, but this doesn't always guarantee better performance. Even if SPF is flattened, there are still character length restrictions (512 bytes for UDP queries), which may cause SPF validation failures.

When using SPF flattening, any provider change (adding a new email-sending service or changing mail servers) requires manual updates to the SPF record. This increases administrative overhead and the risk of misconfiguration.

A flattened SPF record can become too large, exceeding the 255-character limit per SPF string or the 512-byte DNS response limit. This can invalidate the record entirely, making SPF fail for all emails.

SPF flattening creates a large number of IP addresses in a single SPF record, which can lead to delays in DNS resolution, increasing email delivery times or causing timeouts.

Instead of flattening, continue using include mechanisms, which dynamically fetch the latest IPs from email service providers.

Some providers offer automatic SPF compression tools that help reduce the number of lookups without full flattening.

Since SPF alone isn't foolproof, ensure you have DKIM (DomainKeys Identified Mail) and DMARC (Domain-based Message Authentication, Reporting & Conformance) set up for robust email authentication.

For large organizations, using a subdomain-based SPF approach for different services can help distribute DNS lookup loads.

Regularly audit SPF records to ensure they are not exceeding limits, and monitor authentication results using DMARC reporting.

If you're using Your DMARC, you can:
✅ Check your current SPF record for errors.
✅ Receive alerts if SPF lookup limits are exceeded.
✅ Get automatic recommendations on optimizing SPF settings.
✅ Use advanced DMARC reporting to track SPF-related issues.

💡 Try Your DMARC’s SPF Checker Now

Only in very specific cases where email servers are static and unlikely to change. However, it's generally discouraged for cloud-based email services.

Use an SPF record checker tool (like the one in Your DMARC) to analyze your SPF record and see if direct IPs are being used instead of include mechanisms.

If your SPF record exceeds 512 bytes, email servers may reject it or ignore it, leading to email deliverability issues.

No, you should only have one SPF record per domain. If you need multiple sources, include them within a single SPF entry.

SPF was first introduced in 2003 as an email authentication method. That means it's been around for over 20 years, constantly evolving to keep up with modern email security threats! 🚀

✅ Which of the following is a valid SPF record?

(Answer: Option 1 is correct! Option 3 is incorrect because spf=v1 is not a valid syntax.)

While SPF flattening might seem like a quick fix, it creates more problems than it solves. Instead, rely on dynamic includes, DMARC, and proper SPF management tools to ensure secure and error-free email authentication.

👉 Use Your DMARC’s SPF Analyzer to Optimize Your SPF Record Today!