Your SPF record might be sabotaging your email deliverability - and you don’t even know it. While most organizations focus on DMARC policies, a hidden SPF misconfiguration can cause legitimate emails to fail authentication and land in spam.

The culprit? The SPF 10-lookup limit - a hard cap that silently breaks authentication when exceeded, especially if you use multiple ESPs, marketing tools, and cloud senders.

Understanding the SPF 10-Lookup Limit

SPF (Sender Policy Framework) tells receivers which hosts may send mail for your domain. Per RFC 7208, SPF evaluation may perform at most 10 DNS lookups. Exceed it and receivers should treat SPF as permerror.

When that happens, you get:

  • Immediate DMARC authentication failures
  • Legitimate emails marked as spam
  • Deliverability drops and reputation damage

What Counts as a Lookup?

Mechanisms/modifiers that trigger DNS queries:

  • include:
  • a (without a literal host)
  • mx
  • exists
  • redirect=

Each include: can cascade into more include:s - your lookup budget can evaporate fast.

Common SPF Mistakes

“Include Everything” SPF

v=spf1 include:_spf.google.com include:mailchimp.com include:spf.protection.outlook.com include:amazonses.com ~all

Looks tidy, but often explodes past 10 lookups due to nesting.

Legacy Provider Accumulation

Old providers left in the record keep burning lookups.

Nested Include Chains

Some ESPs reference multiple internal SPF records - each adding more lookups.

Advanced SPF Optimization Strategies

1) IP Address Flattening

Replace heavy include:s with their current IP ranges (where stable and contractually documented).

Before

v=spf1 include:_spf.google.com include:mailchimp.com ~all

After

v=spf1 ip4:209.85.128.0/17 ip4:64.233.160.0/19 ip4:198.2.128.0/18 ~all

This can drop multiple lookups to zero - but requires maintenance when providers change IPs.

2) SPF Delegation via Subdomains

# Root
example.com: v=spf1 include:_spf.google.com redirect=spf.marketing.example.com

# Marketing subdomain
spf.marketing.example.com: v=spf1 include:mailchimp.com include:servers.mcsv.net ~all

# Support subdomain
spf.support.example.com: v=spf1 include:mail.zendesk.com ~all

3) Regular SPF Auditing

  • Remove unused includes/providers
  • Measure lookup count (target ≤ 8 to keep headroom)
  • Validate provider SPF changes quarterly

Implementation Plan (SMB-friendly)

  1. Week 1: Inventory providers; remove dead includes
  2. Week 2: Flatten the noisiest providers (document IPs)
  3. Week 3: Delegate heavy stacks to subdomains
  4. Week 4: Monitor DMARC pass rates & inbox placement

SPF + DMARC: Why It Matters

DMARC needs SPF or DKIM in alignment. If SPF frequently permerrors, you’re over-relying on DKIM - a single point of failure. Healthy SPF raises DMARC pass rates and stability.

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FAQ

How do I check my lookup count? Use DMARCFlow’s SPF checker (or trace via dig) and count each DNS-resolving mechanism.

Can I publish multiple SPF records? No. Exactly one TXT SPF record at the root. Merge/flatten instead.

What if I exceed 10? Receivers can return permerror → DMARC often fails → lost inbox placement.

Is flattening always best? It’s effective but requires maintenance. Consider subdomain delegation for very dynamic providers.

Want to see how protected your domain really is? Try the free DMARCFlow domain scan and get an instant report.