Summary
SPF flattening is primarily needed when an SPF record exceeds the 10 DNS lookup limit due to numerous includes, often from third-party services. However, correct SPF configuration, subdomain management, and focusing solely on return paths can mitigate the need. Validation involves checking the 'Received-SPF' header, using tools like `dig`, `nslookup`, online SPF checkers, and analyzing DMARC reports. While flattening addresses lookup limits, simplifying records, subdomain strategies, and a DMARC 'reject' policy are recommended alternatives to avoid management complexities and improve email deliverability. Improper SPF setup can lead to emails being marked as spam.
Key findings
- DNS Lookup Limit: SPF records have a limit of 10 DNS lookups; exceeding this necessitates action.
- Validation Tools: SPF records can be validated via 'Received-SPF' headers, `dig`, `nslookup`, online checkers, and DMARC reports.
- Return Path Focus: SPF records should primarily include services using the domain's return path.
- Alternative Strategies: Simplifying records, subdomain strategies, and DMARC 'reject' policies are preferred alternatives to SPF flattening.
- Deliverability Impact: Incorrect SPF setup impacts email deliverability, causing emails to be marked as spam.
Key considerations
- Subdomain Management: Implement better subdomain management for improved SPF configuration and organization.
- Complexity of Flattening: SPF flattening can introduce management challenges due to IP address changes.
- Service Return Paths: Carefully check the return paths of each service before including it in the SPF record.
- DMARC Policy: Consider implementing a DMARC 'reject' policy to prevent unauthorized sending and reduce the need for SPF adjustments.
- Last Resort: SPF flattening should be considered a last resort after other simplification strategies have been exhausted.
What email marketers say
7 marketer opinions
SPF flattening is primarily needed when an SPF record exceeds the limit of 10 DNS lookups due to numerous 'include' statements for third-party senders. Validation involves verifying the SPF record's syntax and lookup count using tools like online checkers, `dig`, or DMARC reports. While flattening can resolve lookup issues, simplifying SPF records and exploring subdomain strategies are recommended alternatives to avoid management complexities. Incorrect SPF setup can lead to deliverability issues, including emails being marked as spam.
Key opinions
- Lookup Limit: SPF flattening is necessary when an SPF record surpasses the 10 DNS lookup limit.
- Validation Tools: SPF records can be validated using online SPF checkers, the `dig` command, or DMARC reports.
- Alternative Strategies: Simplifying SPF records or using subdomain strategies are preferred over SPF flattening to reduce complexity.
- Deliverability Impact: Improper SPF setup can negatively impact email deliverability, leading to emails being marked as spam.
Key considerations
- Complexity of Flattening: SPF flattening can introduce management challenges due to IP address changes.
- Subdomain Strategy: Explore subdomain strategies to isolate third-party senders and manage SPF records more effectively.
- DMARC Reports: Utilize DMARC reports to gain insights into SPF validation results and identify potential issues.
- Last Resort: SPF flattening should be considered as a last resort after other simplification strategies have been exhausted.
Marketer view
Email marketer from MXToolbox shares that SPF flattening should be used as a last resort. Where possible investigate a subdomain solution so messages from third party providers use different SPF records.
31 Aug 2023 - MXToolbox
Marketer view
Email marketer from StackExchange answers that not setting up SPF correctly or exceeding the limits can lead to emails being marked as spam, potentially damaging sender reputation and affecting email deliverability. SPF flattens helps minimize the risks.
19 Jan 2024 - StackExchange
What the experts say
3 expert opinions
SPF flattening might not be needed if SPF is correctly configured with better subdomain management. Focus on ensuring SPF records only include services using the apex domain's return path. Tools like `dig`, `nslookup`, and online SPF checkers can validate SPF records and confirm they adhere to the DNS lookup limit.
Key opinions
- Correct SPF Configuration: Proper SPF configuration and subdomain management can negate the need for flattening.
- Return Path Focus: SPF records should only include services utilizing the apex domain's return path.
- Validation Tools: `dig`, `nslookup`, and online SPF checkers are useful for validating SPF records.
Key considerations
- Service Return Paths: Check the return path of each service before adding it to the SPF record.
- DNS Lookup Limit: Ensure the SPF record does not exceed the 10 DNS lookup limit.
- Subdomain Management: Implement better subdomain management for improved SPF configuration.
Expert view
Expert from Email Geeks explains that if SPF is configured correctly, SPF flattening might not be necessary, and better subdomain management might be a better solution.
11 Feb 2023 - Email Geeks
Expert view
Expert from Email Geeks explains that different services typically use different return paths, and SPF records are only needed for the return path, not any other domain. He advises to check the return path of mail sent by each service and only include services using the apex domain in the SPF record.
19 Dec 2023 - Email Geeks
What the documentation says
4 technical articles
SPF flattening becomes necessary when a domain exceeds the 10 DNS lookup limit within its SPF record, especially due to numerous third-party services. Validation involves checking the 'Received-SPF' header to verify sending server authorization. It's advisable to avoid SPF flattening by implementing a DMARC policy of reject to block messages from invalid sources entirely.
Key findings
- DNS Lookup Limit: SPF records are limited to 10 DNS lookups.
- SPF Flattening Trigger: Exceeding the DNS lookup limit due to third-party services necessitates SPF flattening.
- Validation Method: SPF records can be validated by examining the 'Received-SPF' header in emails.
- DMARC Policy: Implementing a DMARC policy of 'reject' can help avoid the need for SPF flattening.
Key considerations
- Third-Party Services: Carefully manage the number of third-party services using a domain to avoid exceeding the SPF lookup limit.
- Deliverability Impact: Failing to address SPF limits can lead to deliverability issues.
- DMARC Alternative: Consider implementing a DMARC 'reject' policy as a preventive measure against unauthorized sending.
Technical article
Documentation from Google Workspace Admin Help explains that SPF records have a limit of 10 DNS lookups. If this limit is exceeded, SPF flattening may be needed or the SPF record will fail, causing deliverability issues.
20 Oct 2023 - Google Workspace Admin Help
Technical article
Documentation from Microsoft indicates that SPF flattening becomes essential to maintain email deliverability when a domain utilizes numerous third-party services for sending emails, leading to exceeding the DNS lookup limit within the SPF record.
27 May 2025 - Microsoft
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