Summary
To resolve the MXToolbox SPF record DNS lookup limit exceeded error, a multi-faceted approach is required. The SPF specification (RFC 7208) limits DNS lookups to 10 to prevent DDoS attacks. Minimizing 'include' mechanisms is key. This involves auditing and removing unnecessary 'include' statements, replacing 'include' statements with direct IP addresses (SPF flattening), and utilizing subdomains for different email streams with separate SPF records. For services like HubSpot and Sendgrid, examine the 5321.from address for proper configuration. It's crucial to authorize only necessary domains and be wary of bad advice from ESPs. Maintenance is required with SPF flattening, and remember that the DNS query count matters, not just the domain count.
Key findings
- RFC 7208 Limit: The SPF specification (RFC 7208) limits DNS lookups to 10.
- Reduce Includes: Auditing and minimizing 'include' statements is crucial.
- SPF Flattening: SPF flattening replaces 'include' with direct IPs.
- Subdomain Strategy: Using subdomains helps manage reputation and limits root domain lookups.
- 5321.from Check: Examine the 5321.from for HubSpot/Sendgrid configuration.
- Authorize Domains: Ensure only necessary domains are authorized.
- DNS Query Count: The DNS query count is what matters, not just the number of domains.
Key considerations
- Maintenance: SPF flattening requires ongoing IP address updates.
- Bad Advice: Be cautious of SPF advice from ESPs.
- HubSpot/Sendgrid Specifics: Carefully configure HubSpot/Sendgrid to avoid unnecessary 'include' statements.
- 5321.MailFrom: SPF checks the 5321.MailFrom; ensure proper alignment.
- DDoS Prevention: The lookup limit prevents DDoS attacks.
What email marketers say
11 marketer opinions
To resolve the MXToolbox SPF record DNS lookup limit exceeded error, several strategies are recommended. The primary approaches include reducing the number of 'include' statements in the SPF record, which can be achieved by removing unnecessary or redundant includes, flattening the SPF record by replacing 'include' statements with direct IP addresses, and utilizing subdomains for different email sending services, each with its own SPF record. It's also crucial to use as few includes as possible, ensuring that only domains actively sending email on your behalf are included, and to be aware of the potential maintenance overhead of flattening SPF records due to IP address changes.
Key opinions
- Reduce Includes: Review and minimize the number of 'include' statements in your SPF record by removing unnecessary or redundant entries.
- SPF Flattening: Consider flattening your SPF record by replacing 'include' statements with the actual IP addresses they resolve to.
- Subdomain Usage: Utilize subdomains for different email sending services, assigning each its own SPF record to distribute the lookup load.
- Domain Authorization: Ensure that all domains included in your SPF record are authorized to send email on behalf of your domain.
- DNS Queries: Recognize that the number of DNS queries, not just the number of domains, is what contributes to the lookup limit.
Key considerations
- Maintenance Overhead: Flattening SPF records requires ongoing maintenance to update IP addresses as they change.
- Redundancy Avoidance: Avoid including services you don't need to include. Review and optimize SPF records regularly.
- Subdomain Configuration: If implementing subdomains, ensure that all third-party services are configured to send email from the appropriate subdomain.
- Direct IP Addresses: Using direct IP addresses can reduce lookups but may require more frequent updates as IP ranges change.
- Necessity of Includes: Critically evaluate whether each 'include' is absolutely necessary, as each one can trigger further DNS queries.
Marketer view
Email marketer from EmailQuestions responds it's not a matter of the number of domains, it's a matter of the number of DNS queries that are required to resolve the SPF record. This is why it is essential to review and ensure each 'include' is absolutely necessary. It's also worth noting that each 'include' can itself include further DNS queries, which add to the total count.
15 Dec 2021 - EmailQuestions
Marketer view
Email marketer from MXToolbox states that the simplest solution is to use a dedicated sending domain or subdomain for each vendor. Each should have its own SPF record with ONLY what that vendor requires. You should also avoid using nested includes, such as using Include:vendor2.com in vendor1.com SPF record
20 Jul 2024 - MXToolbox
What the experts say
9 expert opinions
To address the MXToolbox SPF record DNS lookup limit exceeded error, experts recommend several key strategies. Primarily, it's crucial to reduce the number of 'include' statements in your SPF record by auditing and removing unnecessary entries, as excessive use of 'include:' is a common mistake. For HubSpot and Sendgrid, check the 5321.from address to determine if they can be removed or if a specific record for that domain is needed instead of the base domain. Avoid publishing SPF records for domains other than those in the 5322.from. Using subdomains for different email types (e.g., marketing vs. transactional) can also help manage reputation and control, and potentially limit SPF lookups on the root domain.
Key opinions
- Reduce Includes: Auditing and minimizing the number of 'include' statements is crucial to staying within the DNS lookup limit.
- Check 5321.from: For services like HubSpot and Sendgrid, examine the 5321.from address to determine the correct SPF record configuration.
- Subdomain Strategy: Using subdomains for different email streams (marketing, transactional) improves control and can limit SPF lookups on the root domain.
- ESPs and SPF Advice: Be cautious of SPF advice from ESPs, as some may provide incorrect recommendations.
- 5321 vs. 5322: Avoid publishing SPF records for domains other than those used in the 5322.from address.
Key considerations
- HubSpot/Sendgrid Setup: Carefully examine HubSpot and Sendgrid configurations to ensure you're not using unnecessary 'include' statements at the root domain level.
- Domain Alignment: Understand that SPF checks the 5321.MailFrom header, not the From: header; ensure proper alignment for deliverability.
- Root Domain Includes: Evaluate each 'include' statement on the root domain to determine if it's truly necessary or if a more specific record or subdomain is appropriate.
- Bad Advice: Be aware that some ESPs provide bad SPF advice which leads to lookup issues.
Expert view
Expert from Word to the Wise explains that SPF checks the domain in the 5321.MailFrom (Return-Path) header, not the From: header the end-user sees. This is important to understand when configuring SPF records, as the alignment between these domains impacts deliverability.
3 Dec 2022 - Word to the Wise
Expert view
Expert from Word to the Wise explains that a common SPF mistake is using 'include:' statements excessively, which leads to exceeding the 10 DNS lookup limit. She recommends auditing your SPF record to remove unnecessary includes.
29 Feb 2024 - Word to the Wise
What the documentation says
4 technical articles
Documentation across various sources indicates that the MXToolbox SPF record DNS lookup limit exceeded error arises because the SPF specification (RFC 7208) restricts the number of DNS lookups to a maximum of 10 per SPF check to prevent denial-of-service attacks and ensure email delivery efficiency. To resolve this, the primary recommendation is to reduce the number of 'include' mechanisms and nested lookups in the SPF record. This can be achieved by ensuring that only actively used sending providers are included and by considering the use of subdomains to distribute SPF records, thus reducing the lookup load on the primary domain.
Key findings
- RFC 7208 Limit: The SPF specification (RFC 7208) enforces a limit of 10 DNS lookups per SPF check.
- Reduce Includes: Minimizing 'include' mechanisms and nested lookups is essential for resolving the error.
- Subdomain Usage: Utilizing subdomains can help distribute SPF records and reduce lookups on the primary domain.
- Active Providers Only: Ensure that only actively used sending providers are included in the SPF record.
Key considerations
- Nested Lookups: Be aware that nested lookups from 'include' statements contribute to the overall lookup count.
- DDoS Prevention: The lookup limit is in place to prevent denial-of-service attacks.
- Efficient Delivery: Adhering to the lookup limit ensures timely email delivery.
Technical article
Documentation from Google Workspace Admin Help explains that the SPF specification (RFC 7208) limits the number of DNS lookups to 10. This limit is in place to prevent denial-of-service attacks and to ensure timely email delivery. To fix this error, reduce the number of 'include' mechanisms and nested lookups in your SPF record.
29 Nov 2023 - Google Workspace Admin Help
Technical article
Documentation from RFC 7208 specifies that SPF implementations MUST limit the number of mechanisms and modifiers that cause DNS lookups to at most 10 per SPF check, including any lookups caused directly or indirectly by these mechanisms and modifiers.
5 Feb 2023 - RFC Editor
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