7 Essential SPF Flattening Tips for Better DNS Management

SPF flattening is a practical DNS management technique for domains that rely on multiple email vendors, cloud platforms, and third-party senders. A standard SPF record often contains several include statements, but each SPF mechanism that triggers DNS resolution counts toward the DNS lookup limit defined in RFC 7208 by the IETF. When an SPF record exceeds 10 DNS lookups, receiving mail servers may return a PermError, commonly shown as a Too Many Lookups Error, which can cause SPF fail results and harm email deliverability.

The goal of SPF flattening is to convert required record includes and nested records into authorized IP addresses, creating a flattened SPF record that is easier for receivers to evaluate. However, doing this poorly can introduce stale vendor IPs, SPF authentication failure, or unnecessary SPF bloat. These seven tips will help you manage SPF flattening safely while improving SPF compliance, sender verification, and domain security.

Tip #1: Audit Your Current SPF Record Before Flattening

Before starting SPF flattening, audit your current SPF record in full. Many organizations publish an SPF record years ago and continue adding email vendors such as Google Workspace, Microsoft 365, Office 365, SendGrid, Mailchimp, Mandrill, Salesforce, Zendesk, Zoho, Amazon SES, and Sendinblue without reviewing the cumulative SPF lookup count.

Use tools such as MxToolbox, dmarcian, PowerDMARC, dmarc.io, or the MxToolbox SPF Flattening Tool to inspect your current SPF configuration. A Detail Viewer, Domain Overview, or SPF Survey-style report can show whether your SPF record is approaching the DNS lookup limit, already exceeding 10 DNS lookups, or creating a Too Many Lookups Error.

What to Look for During the Audit

Check every SPF mechanism, including include, a, mx, ptr, exists, and redirect. The include mechanisms are often the biggest source of nested records because one third-party sender may reference another SPF record, which may then contain additional record includes.

Also confirm whether you have duplicate SPF records at the same DNS hostname. SPF best practices require only one SPF record per hostname. If you need to remove duplicate records, consolidate them into a single restrictive SPF record that contains only verified senders.

Key Audit Questions

Ask whether each sender is still active, whether each platform is tied to Customer Support, Marketing Automation, billing, or transactional mail, and whether the domain uses DKIM, DMARC, and SPF alignment under an active DMARC policy.

Tip #2: Identify and Remove Unnecessary SPF Includes

SPF flattening works best when you first eliminate unnecessary entries. Flattening a bloated SPF record only turns unnecessary nested records into unnecessary IP addresses. This may temporarily reduce DNS queries, but it increases manual overhead and makes maintaining SPF records more difficult.

Review all third-party senders and confirm whether they still send mail for your domain. Retired systems, old CRMs, unused help desk tools, and abandoned email vendors are common sources of SPF bloat. If your business no longer uses a vendor, remove its include from the SPF record before creating a flattened SPF record.

Reduce SPF Bloat Before It Becomes Risk

Excessive record includes increase the chance of hitting the DNS lookup limit. Once your SPF record exceeds 10 DNS lookups, mail receivers may return a Too Many Lookups Error, which can lead to SPF authentication failure. That failure may also affect your SPF pass rate, especially if your DMARC policy depends on SPF authentication rather than DKIM.

Tim Draegen and Asher Morin have both contributed to broader industry education around DMARC, SPF, and DNS-based authentication, and one recurring lesson is simple: only authorize what you actually use. Fewer third-party senders means fewer nested records, fewer IP addresses to maintain, and a cleaner SPF mechanism chain.

Tip #3: Convert Required Includes into IP Addresses Carefully

The core of SPF flattening is converting necessary include statements into IP addresses. For example, if your SPF record contains an include for SendGrid or Amazon SES, a flattening process resolves the vendor’s nested records and extracts the authorized IP addresses. These IP addresses are then inserted directly into the flattened SPF record.

This approach reduces DNS lookups because mail receivers no longer need to traverse multiple nested records. However, flattening must be done carefully. Vendor IPs can change without notice, especially on shared sending infrastructure. If you flatten once and never update the result, your flattened SPF record may become stale, causing legitimate mail to fail sender verification.

Preserve the Correct SPF Mechanism Logic

When converting includes into IP addresses, preserve the intended SPF mechanism behavior. Do not mix hard enforcement and soft enforcement casually. For example, a softfail may be expressed with ~all, while a stricter policy may use the SPF all mechanism with -all. A domain using -all should be especially cautious because stale IP addresses can cause immediate SPF fail results for legitimate mail.

Manual Flattening Risks

Manual SPF flattening may seem simple, but it creates long-term operational risk. You must track every vendor’s DNS changes, update the SPF record, and ensure the flattened SPF record remains below the DNS lookup limit and valid under RFC 7208.

Tip #4: Keep SPF Records Under the 10 DNS Lookup Limit

The most common reason organizations use SPF flattening is to stay below the 10 DNS lookups allowed by RFC 7208. The DNS lookup limit applies during SPF evaluation, and mechanisms such as include, a, mx, ptr, exists, and redirect can contribute to the total.

If the SPF lookup count exceeds 10 DNS lookups, the receiving server should return a PermError. In practical terms, this often appears as a Too Many Lookups Error. That error can reduce email deliverability because SPF authentication cannot complete reliably.

Manage Nested Records Proactively

Nested records are the hidden danger. Your SPF record may appear to have only four or five includes, but each third-party sender can reference additional nested records. Google, Microsoft 365, Mailchimp, Salesforce, and other email vendors may each publish SPF records that expand into multiple lookups.

SPF flattening reduces reliance on these nested records by publishing IP addresses directly. Still, a flattened SPF record can become too long or fragmented if not managed properly. DNS TXT records have practical length considerations, so keeping the SPF record concise matters.

Tip #5: Automate SPF Flattening to Prevent Stale IP Data

Automation is the safest way to perform SPF flattening at scale. A modern SPF flattening tool can resolve third-party sender includes, detect vendor IPs, rebuild the flattened SPF record, and keep it automatically updated. This reduces manual overhead and supports maintenance-free SPF operations.

Solutions from vendors such as PowerDMARC, dmarcian, MxToolbox, and powerspf.com may provide automatic SPF monitoring, automated SPF reconstruction, and real-time SPF preview features. These capabilities help administrators see how an SPF record will look before publishing it to DNS.

Why Automation Matters

Third-party senders often change their sending IP addresses as they expand infrastructure or rebalance traffic. Without ongoing monitoring, a flattened SPF record can quickly drift from the vendor’s current SPF configuration. That drift may cause SPF authentication failure, lower the SPF pass rate, and create avoidable support issues.

Automated SPF flattening also helps maintain SPF compliance by checking the DNS lookup limit continuously. If an update risks exceeding 10 DNS lookups or introducing a Too Many Lookups Error, the system can alert administrators before mail flow is affected.

Tip #6: Monitor DNS Changes from Third-Party Email Senders

Even after SPF flattening, DNS management does not stop. Your third-party senders may update their SPF record, add new nested records, retire old IP addresses, or move to new shared sending infrastructure. These changes can affect your flattened SPF record, even though your own DNS zone has not changed.

Use automatic SPF monitoring to track changes from email vendors such as Google Workspace, Office 365, SendGrid, Zendesk, Zoho, Amazon SES, and Sendinblue. If a vendor adds new IP addresses, your SPF flattening workflow should detect the change and update the flattened SPF record quickly.

Use Segmentation Where Appropriate

Subdomain segmentation can reduce risk. For example, you might use one subdomain for Marketing Automation, another for Customer Support, and another for transactional mail. Each subdomain can have its own SPF record, DKIM keys, and DMARC alignment strategy.

SPF delegation may also help in some environments, allowing a trusted service to manage SPF-related DNS records while the organization maintains control over domain security. This is useful when multiple teams manage third-party senders and need consistent SPF best practices.

Tip #7: Test and Validate Your Flattened SPF Record Regularly

Every flattened SPF record should be tested before and after publication. Use MxToolbox, dmarcian, PowerDMARC, or the MxToolbox SPF Flattening Tool to confirm that the SPF record is syntactically valid, stays under the DNS lookup limit, and does not trigger a Too Many Lookups Error.

Validation should check more than syntax. Send test messages through all verified senders, including Google, Microsoft 365, SendGrid, Mailchimp, Mandrill, Salesforce, Zendesk, Zoho, Amazon SES, and any other active platforms. Confirm that SPF authentication passes, DKIM signs correctly, and DMARC evaluates as expected.

What Regular Validation Should Confirm

A complete validation process should verify that the flattened SPF record contains current IP addresses, avoids unnecessary nested records, respects the 10 DNS lookups requirement, and uses the right final SPF all mechanism, such as -all for strict enforcement or ~all for softfail.

Regular testing also helps identify stale vendor IPs, broken include mechanisms, invalid DNS syntax, and hidden SPF limitations. When combined with ongoing monitoring and an SPF flattening tool, testing ensures your SPF record remains reliable, secure, and aligned with modern DNS-based authentication practices.