Summary
The consensus is that adhering to the 10 DNS lookup limit in SPF records is crucial for email deliverability. Exceeding this limit can cause SPF authentication to fail ('permerror'), leading to emails being rejected or marked as spam. While some email servers may be more lenient, strict adherence to the RFC specification is recommended. Strategies to manage the lookup count include flattening SPF records (converting 'include' statements to direct A records), carefully managing includes from providers, and using tools to avoid manual flattening due to IP changes. Regularly checking SPF records, testing, and considering alternative authentication methods like DKIM are also advised.
Key findings
- SPF Authentication Failure: Exceeding 10 DNS lookups causes SPF authentication to fail ('permerror').
- Deliverability Impact: SPF failures negatively impact email deliverability, potentially leading to email rejection or spam classification.
- Strict vs. Lenient Servers: Some email servers enforce SPF record requirements more strictly than others.
- Manual Flattening Risks: Manual flattening carries the risk of IP address changes in includes.
Key considerations
- Flattening SPF Records: Flatten SPF records to reduce the number of DNS lookups.
- Manage Provider Includes: Carefully manage includes from providers to control DNS lookup contributions.
- Use Tools for Flattening: Utilize tools for flattening to avoid risks associated with manual methods.
- Test SPF Records: Regularly check and test SPF records to ensure validity.
- Implement DKIM: Consider implementing DKIM as a supplementary authentication method.
What email marketers say
7 marketer opinions
The 10 DNS lookup limit in SPF records is a critical factor for email deliverability. Exceeding this limit causes SPF authentication to fail ('permerror'), leading to emails being rejected or marked as spam. Flattening SPF records, checking for unnecessary includes, and using tools to manage DNS lookups are recommended strategies to stay within the limit. Employing DKIM as an alternative or supplementary authentication method can also mitigate deliverability issues arising from SPF failures.
Key opinions
- SPF Failure: Exceeding 10 DNS lookups results in SPF authentication failure ('permerror').
- Deliverability Impact: SPF failures negatively impact email deliverability, potentially causing emails to be rejected or marked as spam.
- Hosting Provider Issues: Hosting providers' SPF records may contain unnecessary includes (e.g., Google IPs) contributing to the lookup count.
- Flattening Benefits: Flattening SPF records combines includes to stay within the 10 lookup limit.
Key considerations
- Manual Flattening Risks: Manual flattening is discouraged due to IP address changes in includes; use tools instead.
- Unnecessary Includes: Regularly check for and remove unnecessary 'include' directives in SPF records.
- Tool Utilization: Use SPF flattening and lookup management tools to maintain records.
- Alternative Authentication: Implement DKIM as a complementary authentication method to mitigate SPF failures.
- Testing SPF Records: Test that SPF records are valid and under the 10 lookup limit.
Marketer view
Email marketer from StackOverflow responds that exceeding the 10 DNS lookup limit causes an SPF 'permerror' and advises checking how many lookups you have, and flattening your record if required. If you can't flatten the record, try other authentication methods like DKIM to reduce dependence on SPF alone.
1 Apr 2023 - StackOverflow
Marketer view
Email marketer from scotthelme.co.uk explains the 10 DNS lookup limit and suggests that exceeding it is a very bad idea. Scott Helme explains that mail servers will stop evaluating your SPF record the moment the 10 lookup limit is breached, and typically reject your emails due to SPF failing to pass. The best approach is to stay well below the limit.
6 Oct 2022 - scotthelme.co.uk
What the experts say
4 expert opinions
The 10 DNS lookup limit in SPF records is crucial for email authentication, as exceeding it can lead to SPF failing. Although some mail servers may be lenient, strict adherence to the RFC specification is recommended. Strategies to stay within the limit include flattening the SPF record, which involves manually resolving lookups to A records instead of using includes, and carefully managing the includes from your providers to understand their DNS lookup contributions.
Key opinions
- SPF Authentication Failure: Exceeding 10 DNS lookups causes SPF authentication to fail, according to the specification.
- Recipient Variability: Some email recipients are stricter than others in enforcing SPF record requirements.
- Importance of Staying Within Limit: Staying under the 10 DNS lookup limit is essential for SPF to function correctly.
Key considerations
- Manual Flattening: Flatten the SPF record by replacing includes with A records to avoid exceeding the limit.
- Provider Management: Work with providers to manage includes and understand their DNS lookup contributions.
Expert view
Expert from Spam Resource explains that you have to stay under 10 DNS lookups within your SPF record, or it won't work. It is recommended to flatten the SPF record by manually doing the lookups and putting in A records instead of includes. This avoids any possible DNS lookup issues.
12 Jan 2024 - Spam Resource
Expert view
Expert from Word to the Wise responds that with SPF, you must make sure you're under the 10 DNS lookup limit. Laura Atkins recommends working with your providers to manage the includes, and understanding what DNS lookups each include is contributing to the overall count. If you can't keep it under 10, you have to flatten the SPF record.
6 Jun 2024 - Word to the Wise
What the documentation says
3 technical articles
The SPF standard mandates a strict limit of 10 DNS lookups per SPF record. Exceeding this limit results in SPF authentication failures, as receiving mail servers often ignore SPF results that breach the limit. This impacts email deliverability and can cause temporary errors due to DNS timeouts or server load. The 10 lookup limit includes nested lookups from 'include:' mechanisms. SPF queries are resource intensive, and excessive queries can lead to denial-of-service issues and slow email processing.
Key findings
- Hard Limit: SPF has a hard limit of 10 DNS lookups.
- Authentication Failure: Exceeding the limit causes SPF authentication to fail.
- Deliverability Impact: SPF failures negatively impact email deliverability.
- Resource Intensive: SPF queries are resource intensive, potentially causing DNS timeouts and server load issues.
Key considerations
Technical article
Documentation from SPF-record.com explains that the SPF standard dictates a limit of 10 DNS lookups. Exceeding this limit can cause SPF authentication to fail, as receiving mail servers are likely to ignore SPF results from records exceeding the limit. This can negatively impact email deliverability.
9 May 2024 - SPF-record.com
Technical article
Documentation from dmarcian shares that SPF has a hard limit of 10 DNS lookups. This limit includes any nested lookups from 'include:' mechanisms. Exceeding this limit will cause the SPF check to fail. This happens because SPF queries are resource intensive, and too many queries could lead to denial-of-service issues and slow email processing.
6 May 2025 - dmarcian
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