Why is my SPF record too long and how to manage DNS TXT record length limits?
Michael Ko
Co-founder & CEO, Suped
Published 15 Jul 2025
Updated 19 Aug 2025
8 min read
When managing email deliverability, the Sender Policy Framework (SPF) record is a critical component for authentication. It helps receiving mail servers verify that incoming mail from a domain is sent from a server authorized by that domain's administrators, playing a crucial role in preventing email spoofing and phishing attacks. However, many organizations encounter issues when their SPF record becomes too long, leading to validation failures and impacting email deliverability.
The length of your SPF record is primarily governed by two distinct limits: the character string length for DNS TXT records and the DNS lookup limit. Understanding both of these is essential for diagnosing why your SPF record might be failing and ensuring your legitimate emails reach the inbox. We will explore how these limits affect your email setup and what practical steps you can take to manage them effectively.
SPF records are published as TXT records in your domain's DNS. While a single TXT record can theoretically be quite large (up to 4,000 characters for some DNS providers like Amazon Route 53), the crucial detail lies in how individual strings within that record are handled. Each character string within a TXT record cannot exceed 255 characters (bytes), as per RFC 7208. If your SPF record's value exceeds this, it must be split into multiple quoted strings.
For example, if your SPF record is 300 characters long, it would typically be represented as two separate strings, like "v=spf1 include:example1.com ..." "include:example2.com ~all". Most DNS providers automatically handle this splitting for you when you enter a long string, but it is important to be aware of this underlying mechanism. You can find more information about TXT record string limitations if you are troubleshooting.
The second and often more problematic limit is the 10 DNS lookup limit. An SPF record should not require more than 10 DNS lookups during its evaluation process. Each time an SPF mechanism like include, a, mx, or ptr requires a DNS query to resolve, it counts towards this limit. Exceeding this limit results in an SPF PermError, which means the receiving server cannot fully validate your SPF record, often leading to legitimate emails being marked as spam or rejected. Understanding how important the 10 DNS lookup limit is is vital for deliverability.
Why SPF records become too long
The primary reason SPF records become too long, especially in terms of DNS lookups, is the proliferation of email sending services. Many businesses use multiple third-party providers for different email functions, such as marketing emails, transactional emails, customer support, and internal communications. Each of these services often requires adding an include mechanism to your SPF record, pointing to their respective SPF records.
For example, you might have separate include directives for SendGrid, Mailchimp, and Microsoft 365. Each of these includes might, in turn, reference multiple other domains, quickly escalating your DNS lookup count. Additionally, using mechanisms like mx or ptr, especially ptr, can consume multiple lookups themselves, further contributing to the problem. The effect of 'a' records on DNS lookups can also be surprising.
Having a long SPF record or one that exceeds the 10-lookup limit directly impacts your email deliverability. When an SPF record cannot be fully evaluated, receiving mail servers may treat your emails with suspicion, leading to them being sent to the spam folder, quarantined, or even outright rejected. This can significantly affect your communication efforts and domain reputation. Learn more about how broken SPF records affect deliverability.
Common issues
Multiple ESPs: Using numerous email service providers, each requiring its own include.
Old records: Accumulation of outdated or unnecessary entries over time.
Subdomain setup: Incorrect SPF record configuration for subdomains or aliases.
Impact on deliverability
Authentication failure: Emails fail SPF checks, leading to rejection or spam classification.
Reputation damage: ISPs view the domain as less trustworthy, affecting all email campaigns.
Bounce rates: Increased bounces due to invalid or unreadable SPF records.
Strategies to manage SPF record length
To effectively manage SPF record length, particularly the DNS lookup limit, you should first identify and consolidate your existing email sending services. Review all include mechanisms and remove any that are no longer in use. If multiple services use the same underlying infrastructure, you might only need a single include. For example, if both your marketing and transactional email providers route through the same large email sender, you might only need one include statement for that major sender. This requires careful auditing of your email infrastructure to avoid inadvertently breaking legitimate sending.
Another powerful strategy is SPF flattening (also known as blocklist flattening or DNS blocklist flattening). This involves replacing specific include mechanisms with the actual IP addresses or IP ranges those includes resolve to. This eliminates the need for additional DNS lookups when the SPF record is evaluated. While effective, manual flattening requires diligent maintenance because IP addresses of third-party services can change, requiring you to constantly update your SPF record. For this reason, many organizations use services that automatically flatten and manage their SPF records.
When your SPF record exceeds the 255-character string limit for a single TXT record, you can split it into multiple quoted strings. Most DNS providers will automatically combine these strings into a single record when queried. For example, instead of one very long string, you would enter "v=spf1 include:spf1.com" "include:spf2.com ~all". This method addresses the string length limit, but it does not reduce the number of DNS lookups. For that, you will still need to consolidate entries or consider SPF flattening.
Implementing solutions and best practices
Regularly auditing your SPF record is crucial. As your organization adopts new email services or discontinues old ones, your SPF record should be updated to reflect these changes. An outdated SPF record can either cause legitimate emails to fail authentication (if necessary includes are missing) or contribute to lookup overages (if unused includes remain). Consider scheduling periodic reviews, perhaps quarterly or semi-annually, to keep your SPF record clean and efficient.
Before implementing any changes to your SPF record, it is essential to test it thoroughly. Various online SPF validation tools can help you check for syntax errors, DNS lookup counts, and overall record validity. Testing helps you catch potential issues before they impact your live email flow. For a comprehensive check, refer to Google's guidelines on SPF records which emphasize the 10-lookup limit.
DMARC (Domain-based Message Authentication, Reporting, and Conformance) is another vital email authentication protocol that builds upon SPF and DKIM. While DMARC doesn't directly solve SPF record length issues, it provides valuable reporting that can alert you to SPF authentication failures. By analyzing DMARC reports, you can identify if your SPF record is causing problems for email recipients and take corrective action. This makes DMARC an indispensable tool for maintaining email deliverability.
Important consideration
Be cautious when modifying your SPF record. Incorrectly formatted or overly aggressive SPF policies can lead to legitimate emails being rejected. Always make changes during off-peak hours and monitor your email delivery closely afterward. If you are unsure, consult with an email security or DNS expert. Using an SPF flattening service can mitigate these risks.
Views from the trenches
Best practices
Keep your SPF record concise and only include necessary authorized sending sources.
Regularly audit your SPF record to remove outdated or unused include mechanisms and IP addresses.
Utilize SPF flattening services to reduce DNS lookups and avoid the 10-lookup limit.
Implement DMARC to monitor SPF authentication results and identify any failures.
Common pitfalls
Adding too many include statements, causing the 10 DNS lookup limit to be exceeded.
Failing to remove SPF entries for old email service providers, creating unnecessary lookups.
Using MX or PTR mechanisms, which often consume multiple DNS lookups unnecessarily.
Not splitting TXT records into multiple strings when exceeding the 255-character per string limit.
Expert tips
Use CNAME alternatives for domain verification whenever possible to minimize TXT record usage on the root domain.
Remember that the byte size limitation for TXT records applies to the entire record, not just the SPF part.
Root TXT records are valuable space; avoid using them if there's an alternative verification method.
Prioritize consolidating your email sending infrastructure to simplify SPF management.
Expert view
Expert from Email Geeks says a seemingly short SPF record might still be long in bytes when other TXT records are considered.
Sep 4, 2019 - Email Geeks
Expert view
Expert from Email Geeks says removing unnecessary Google site verification TXT records can help shorten the total TXT record length.
Sep 4, 2019 - Email Geeks
Final thoughts on SPF management
Managing SPF record length is a critical aspect of email deliverability. While the 255-character string limit for TXT records can often be resolved by splitting the record, the 10 DNS lookup limit requires a more strategic approach, typically involving consolidation or SPF flattening. Proactive management of your SPF record ensures that your emails are properly authenticated, reducing the risk of them being flagged as spam or rejected by receiving mail servers. Regularly auditing your DNS records and utilizing tools like DMARC for monitoring will help maintain a healthy email sending reputation and maximize inbox placement.
SendGrid, 
Mailchimp, and 
Microsoft 365. Each of these includes might, in turn, reference multiple other domains, quickly escalating your DNS lookup count. Additionally, using mechanisms like mx or ptr, especially ptr, can consume multiple lookups themselves, further contributing to the problem. The effect of 'a' records on DNS lookups can also be surprising.
