What Is SPF Flattening? How to Avoid it?

SPF flattening is a method used to simplify an SPF record by replacing all “include” mechanisms with their corresponding IP addresses. The idea behind SPF flattening is to reduce DNS lookups and prevent the “too many DNS lookups” error that often occurs when an SPF record includes multiple third-party services. In simple terms, flattening an SPF record means compiling all those lookups into a single list of IPs.

While this might sound like a quick fix, it often creates more problems than it solves. The moment a third-party service changes its IP addresses, your flattened SPF record can become outdated, leading to email delivery issues or authentication failures. Understanding how to flatten an SPF record is useful, but relying on this method isn’t the best long-term approach for maintaining a healthy, reliable email authentication setup.

Why SPF Flattening Doesn’t Work?

Here are the main reasons why SPF flattening only looks good in theory, whereas in reality, it often turns into technical and operational headaches: 

1. Constant IP Address Changes

Most email and cloud service providers regularly add, remove, or update their sending IP addresses. A flattened SPF record quickly becomes outdated unless you manually track every change. 

For example, if your email provider rotates its outbound IPs and you’ve listed the old ones directly in your SPF record, messages sent from the new IPs will fail SPF checks. As a result, legitimate emails may be flagged as unauthenticated, leading to delivery errors or outright rejection.

2. High Maintenance Effort

Flattened SPF records demand continuous monitoring. Every time a provider updates their infrastructure, you must revise your SPF record. This ongoing maintenance consumes valuable time and increases the chance of configuration drift.

3. Risk of Syntax and Data Errors

Flattened records are long and complex. A single typo in an IP address or a missing delimiter can invalidate the entire SPF record. Even a misplaced space or incorrect IPv6 format can break the setup and disrupt mail flow.

4. Loss of Traceability

Once you replace includes with IPs, you lose visibility into which IPs belong to which service. Future administrators or team members can’t easily tell where each address came from, complicating troubleshooting and updates.

5. Increased Fragility

Because flattening results in massive, rigid SPF records, they are prone to failure. As your organization adds more services, the list grows, making it harder to manage and easier to exceed DNS or character limits.

6. A Temporary solution, Not a Strategy

SPF flattening doesn’t actually fix the root problem; it only hides it. The 10-lookup limit exists to ensure efficient DNS performance. Flattening circumvents it but introduces reliability and accuracy risks that can harm email deliverability long-term.

How to Avoid SPF Flattening?

To avoid flattening your SPF record, you need to ensure your SPF record doesn’t exceed the DNS lookup limit of 10. So, here are ways to stay within this limit:

1. Remove Non-essential SPF Entries

Start by auditing your SPF record and removing entries that no longer serve a purpose. If a vendor’s mail system can’t be aligned for SPF authentication or shows a zero percent SPF pass rate, it’s better to exclude them. Tools like SPF Record Checker can help you identify unnecessary mechanisms and sources that bloat your record. This cleanup instantly reduces DNS lookups and prevents authentication errors.

2. Avoid Using “a” and “mx” Mechanisms

These mechanisms often expand into multiple DNS lookups, eating into your 10-lookup budget without providing much value. If they’re not critical to your sending setup, remove them. Instead, directly reference specific IP addresses or use “includes” from trusted sources.

3. Delete Duplicate or Redundant Mechanisms

Duplicate entries can occur when integrating multiple email vendors or during repeated SPF updates. These redundant entries don’t improve authentication but only increase record length and DNS lookups. 

We recommend conducting regular SPF syntax checks using SPF Raw Checker, which highlights duplication, syntax errors, and other inefficiencies that could impact deliverability.

4. Discard the Top-Level Domain “includes”

Top-level “includes,” such as referencing “include:example.com” instead of its subdomain, can unintentionally authorize thousands of IP addresses. This increases your attack surface and consumes unnecessary lookups. Always include only the subdomain responsible for sending email, ensuring SPF alignment with your Return-Path domain.

5. Use Subdomain Segmentation

If multiple services send on behalf of your primary domain, move each to a dedicated subdomain for SPF authentication. For example, “marketing.yourdomain.com” can handle newsletters while “billing.yourdomain.com” manages invoices. Each subdomain gets its own SPF record and its own 10 DNS lookups, allowing you to scale without SPF record flattening.

6. Audit and Maintain SPF Records Regularly

SPF records aren’t set-and-forget. Review them periodically to remove outdated senders or vendors you no longer use. Schedule audits with DMARC Analyzer to monitor all email sources, detect misalignments, and receive detailed reports on SPF performance. This ongoing maintenance helps you stay within lookup limits and ensures consistent deliverability.

Final Verdict on SPF Flattening

SPF flattening may appear to simplify your SPF record, but in reality, it adds more risk than reliability. Constant IP changes, syntax errors, and maintenance challenges make it an unstable approach for long-term email authentication. Instead of flattening, focus on optimizing your SPF setup with trusted tools that provide accuracy and real-time monitoring. 

EasyDMARC’s SPF Record Checker, DMARC Analyzer, and other authentication tools help you manage records efficiently, stay within the lookup limit, and maintain consistent email deliverability, without the hassle or risk of flattening.

Frequently Asked Questions