Summary
SPF flattening is generally considered necessary when an SPF record approaches or exceeds the 10 DNS lookup limit, a restriction set to prevent denial-of-service attacks. This situation commonly arises when organizations utilize multiple email service providers (ESPs), third-party integrations, or complex SPF configurations. By simplifying the SPF record, flattening helps avoid authentication failures, maintains deliverability, and ensures compatibility with various email receivers. Proactive monitoring of DMARC reports and regular reviews of the SPF record are also recommended to identify and address potential SPF-related issues.
Key findings
- Lookup Limit: The 10 DNS lookup limit, as defined by RFC 7208, is the primary driver for needing SPF flattening.
- Multiple Sources: Using multiple email sending sources (ESPs, third-party services) increases the likelihood of exceeding the lookup limit.
- Deliverability Impact: Exceeding the lookup limit can lead to SPF authentication failures, resulting in reduced email deliverability.
- DMARC Monitoring: Monitoring DMARC aggregate reports helps identify SPF-related issues and the effectiveness of SPF flattening solutions.
- Complexity Factor: Complex SPF records with numerous includes can also contribute to exceeding the lookup limit.
Key considerations
- Record Assessment: Evaluate the complexity of the SPF record and the number of DNS lookups it requires.
- Third-Party Impact: Carefully consider the number and configuration of third-party services integrated with the email setup.
- Proactive Approach: Implement SPF flattening proactively, especially when adding or removing email sending services.
- Regular Monitoring: Monitor DMARC reports to identify any SPF-related issues promptly.
- Compatibility: Consider SPF flattening to ensure maximum compatibility with different email receivers and prevent potential deliverability problems.
What email marketers say
13 marketer opinions
SPF flattening is generally necessary when an SPF record approaches or exceeds the limit of 10 DNS lookups. This is a common issue when using multiple email service providers (ESPs) or third-party integrations. The process simplifies the SPF record, preventing authentication failures and deliverability problems. Monitoring DMARC reports is also recommended to identify and correct any SPF misconfigurations.
Key opinions
- Lookup Limit: Exceeding the 10 DNS lookup limit in an SPF record is the primary reason for needing SPF flattening.
- Multiple ESPs: Using multiple email service providers or third-party services significantly increases the likelihood of surpassing the lookup limit.
- Deliverability Impact: Unflattened SPF records that exceed the lookup limit can lead to email authentication failures and reduced deliverability.
- DMARC Monitoring: Monitoring DMARC reports is crucial to identifying SPF-related issues and assessing the effectiveness of SPF flattening.
- Proactive Approach: Reviewing and flattening SPF records proactively is advisable, especially when adding or removing email sending services.
Key considerations
- Record Complexity: Evaluate the complexity of your SPF record and the number of DNS lookups before implementing SPF flattening.
- Third-Party Services: Consider the number and configuration of third-party services integrated with your email setup.
- Monitoring: Implement continuous monitoring of DMARC reports to identify and address any SPF-related issues promptly.
- Alternative Solutions: Explore alternative solutions like using a universal SPF record before resorting to SPF flattening.
- Regular Reviews: Perform regular reviews of your SPF record to ensure it remains optimized and compliant with DNS lookup limits.
Marketer view
Email marketer from MailerLite clarifies that a poorly configured SPF record (e.g., exceeding lookup limits) can negatively impact email deliverability. SPF flattening can help maintain deliverability by simplifying the record.
14 Nov 2024 - MailerLite
Marketer view
Email marketer from DNSimple advises to review and flatten your SPF record proactively if you add or remove email sending services. This ensures the record remains optimized and compliant with the DNS lookup limit.
27 Dec 2022 - DNSimple
What the experts say
2 expert opinions
SPF flattening is essential when an SPF record nears or surpasses the 10 DNS lookup limit, typically due to multiple sending sources. This avoids SPF failures and maintains email deliverability.
Key opinions
- DNS Lookup Limit: SPF flattening is required when DNS lookups in an SPF record exceed 10.
- Multiple Senders: Organizations with multiple email sending sources commonly need SPF flattening.
- Deliverability Issues: Failure to flatten SPF records approaching the limit can result in deliverability problems.
Key considerations
- Assessment: Assess the number of sending sources and their impact on SPF record complexity.
- Monitoring: Continuously monitor the SPF record and deliverability rates to identify issues.
- Implementation: Implement SPF flattening proactively to prevent potential deliverability problems.
Expert view
Expert from Word to the Wise answers that SPF flattening is a useful tool when an organization has multiple sending sources and their SPF record approaches the 10 DNS lookup limit, which can cause deliverability issues.
27 Mar 2022 - Word to the Wise
Expert view
Expert from Spam Resource explains that SPF flattening becomes necessary when the number of DNS lookups required by your SPF record exceeds the limit of 10, leading to SPF failures and potential deliverability problems.
7 Apr 2022 - Spam Resource
What the documentation says
4 technical articles
SPF flattening is necessary when an SPF record exceeds or approaches the 10 DNS lookup limit imposed by RFC 7208. This limit, designed to prevent denial-of-service attacks, is often reached when organizations use multiple email sources (including third-party services). Flattening reduces the number of DNS lookups, preventing SPF validation failures and deliverability issues.
Key findings
- RFC Limit: RFC 7208 mandates a maximum of 10 DNS lookups per SPF check, necessitating flattening when this limit is approached.
- DDoS Prevention: The 10-lookup limit is in place to prevent denial-of-service attacks via excessive DNS queries.
- Multiple Sources: Using multiple email sending sources, including third-party services, significantly increases the likelihood of exceeding the lookup limit.
- Validation Failure: Exceeding the lookup limit can lead to SPF validation failures, causing deliverability problems.
Key considerations
- Lookup Count: Regularly assess the number of DNS lookups required by your SPF record.
- Third-Party Services: Carefully consider the number of third-party services that are included in your SPF record.
- Proactive Flattening: Proactively flatten your SPF record if your organization uses multiple email sources and the lookup count approaches the limit.
- Testing: Test your SPF record after flattening to ensure correct configuration and prevent unintended consequences.
Technical article
Documentation from EasyDMARC explains that SPF flattening becomes necessary when an SPF record exceeds the 10 DNS lookup limit. This limit, set to prevent denial-of-service attacks, can be problematic for organizations using multiple third-party email services.
4 Dec 2023 - EasyDMARC
Technical article
Documentation from Google Workspace Admin advises that if your domain sends email from more than one source (e.g., in-house servers and third-party senders), you should evaluate your SPF record. If the lookups approach 10, consider SPF flattening.
21 Jun 2021 - Google
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