SPF flattening is a last-resort fix for the RFC 7208 10-DNS-lookup limit, safe only for stable, documented IP ranges that you actively monitor. Prefer pruning unused includes first, then moving dynamic senders to dedicated subdomains, then SPF macros. Flattening Microsoft 365 or Google Workspace ranges almost always creates intermittent SPF failures.
When the 10-Lookup Limit Actually Breaks Mail
RFC 7208 section 4.6.4 hard-caps the number of DNS lookups during SPF evaluation at 10. Exceeding it returns a permanent error (PermError). Receivers stop evaluating the record. Depending on your DMARC policy, that can mean rejection, spam folder placement, or unauthenticated treatment. The limit exists to prevent resource exhaustion; it is not a soft guideline.
Most teams hit it after stacking includes for Microsoft 365, Google Workspace, several ESPs, and internal systems. The published guide on the SPF 10 DNS Lookup Limit covers the mechanics. This article owns the decision of whether and how to flatten once you are already over the limit.
How We Analyzed Flattening Trade-offs
We reviewed RFC 7208, Microsoft’s current guidance against flattening include:spf.protection.outlook.com (Microsoft Learn: set up SPF), which says Microsoft’s sending IP addresses change frequently. Claims below rest on that public guidance and the RFC 7208 lookup limit, not on proprietary failure rates.
When Flattening Helps vs When It Risks Deliverability
| Scenario | Flatten? | Why |
|---|---|---|
| Stable, documented vendor IPs that change rarely | Maybe, with monitoring | Pinned IPs stay accurate if you recheck on a schedule |
| Microsoft 365 or Google Workspace | Never | Ranges rotate without notice; Microsoft explicitly warns against flattening their include |
| Major ESPs with frequent IP additions | Avoid | Stale records produce silent SPF failures |
| Under 8 lookups after pruning | No | Pruning is sufficient and safer |
Flattening replaces include: mechanisms with explicit IP addresses. It solves the lookup count immediately but freezes the list. When the provider adds or rotates addresses, your record fails until you manually update it. That failure is often silent until volume drops or DMARC reports show alignment breaks.
Better Alternatives in Priority Order
1. Prune unused mechanisms first
Remove dead includes, unnecessary ptr, and unused mx. Many teams recover under the limit with no other changes. See the step-by-step in How to Fix SPF PermError: Too Many DNS Lookups.
2. Move high-volume or dynamic senders to subdomains
Each subdomain receives its own independent 10-lookup budget. Relaxed DMARC alignment (aspf=r) keeps the subdomain aligned with the organizational domain. This is the cleanest long-term pattern for mixed transactional and marketing traffic. Details appear in SPF, DKIM, and DMARC on Subdomains and the companion Why Marketing and Transactional Email Should Use Separate Subdomains.
3. Use SPF macros where supported
RFC 7208 section 7 macros allow dynamic expansion. Some modern tools and providers support them, reducing the need for static lists. Adoption is still uneven, so test thoroughly.
4. Hosted dynamic SPF management
Services that continuously resolve and republish a flattened or macro-based record can remove manual maintenance. They add a dependency and cost; evaluate only after the first three options are exhausted.
Manual static flattening remains a last resort and only with scheduled revalidation (weekly or on provider change notifications).
Interaction with DMARC Alignment
An SPF PermError fails the SPF check. Even if DKIM passes, DMARC alignment can still fail depending on the policy and whether the From domain aligns. Relaxed alignment helps with subdomains but does not rescue a PermError on the evaluated domain. Review the distinction in DMARC Alignment vs SPF Pass.
ArawaMail and DNS Activation
When you activate sending on a domain, ArawaMail publishes the DKIM, SPF and custom MAIL FROM records it needs, through Cloudflare or, for domains registered with ArawaMail, directly on its own nameservers. It does not perform or recommend SPF flattening. Domain onboarding and sending activation are documented at the platform guides for domain onboarding and sending. Each domain is handled independently, which pairs naturally with a subdomain isolation strategy.
Practical Next Steps
- Run an SPF lookup count on the live record.
- Prune first; retest.
- If still over, identify dynamic includes (Microsoft, Google, major ESPs) and move them to dedicated subdomains.
- Only then consider macros or monitored flattening for any remaining stable ranges.
- Monitor DMARC aggregate reports for new alignment failures after any change.
FAQ
Does SPF flattening improve inbox placement?
No. It only resolves PermError. It does not raise reputation or engagement scores.
How often should a flattened record be rechecked?
At least weekly for any provider that rotates IPs, and immediately after known infrastructure changes. Automated monitoring is preferable.
Can I flatten only part of the record?
Yes. Flatten the stable includes and leave dynamic ones as includes or move them to subdomains. Partial flattening still requires monitoring on the flattened portion.
For the full authentication stack, start with SPF, DKIM, and DMARC explained and the free checks guide.