DNS

Nested SPF Includes

Nested includes occur when an SPF include points to another policy that contains additional includes, multiplying DNS lookup cost.

Intermediate · 7 min read · Reviewed Jul 4, 2026

Quick answer

Nested SPF includes happen when an included domain publishes its own include mechanisms, causing receivers to traverse multiple policy layers. Each layer consumes DNS lookups and adds dependency on third-party DNS maintenance. Deep nesting is a primary reason domains exceed the ten-lookup limit and encounter PermError during authentication.

Beginner explanation

A single include in your SPF record rarely stays single for long. Major email providers publish their own SPF policies that reference additional infrastructure, and those references count against your lookup budget too.

Nested includes are convenient for vendors because they can update IP ranges without asking every customer to edit DNS. For domain owners, however, each extra layer is a hidden dependency that can break without any change on your side.

Learning to see through include chains is a core SPF skill. What looks like one line in your zone file may expand into a tree of DNS queries at evaluation time.

Technical explanation

When a receiver encounters include:spf.vendor.com, it fetches the TXT record at spf.vendor.com and logically merges the mechanisms found there. If that policy contains include:spf.vendor.net, evaluation continues into another domain, incrementing the lookup counter at each step.

Nested includes can also create circular references or redundant paths. While RFC 7208 requires receivers to detect some circularities, operational mistakes such as mutual includes between partner domains still cause PermError or unpredictable results.

Best practice is to periodically resolve the full include tree, remove providers you no longer use, and avoid duplicative includes that authorize the same vendor through multiple paths. Managed include services exist precisely because manually maintaining deep trees across many SaaS tools becomes unsustainable.

Business impact

Nested include failures are especially painful because your DNS record may not have changed when deliverability drops. A vendor updating its own SPF policy can push your domain over the lookup limit overnight.

Teams without visibility into the full chain spend days troubleshooting IP allowlists and content filters when the root cause is indirect DNS dependency several layers deep.

Common mistakes

- Adding both a vendor's legacy and current include macros after a platform migration
- Assuming an include always resolves to IP addresses without checking the vendor's current documentation
- Ignoring nested includes inside redirect targets

How SPF Manager helps

SPF Manager recursively resolves include trees and presents them as a readable dependency map. You can identify which nested paths are redundant, stale, or lookup-expensive without manually querying each hostname.

When vendors change their SPF infrastructure, alerts help you detect drift early so you can adjust your record before receivers start returning PermError or fail results.