Summary
The 'CharacterStringTooLong' error, encountered when managing Sender Policy Framework (SPF) records, typically indicates that the DNS TXT record has exceeded its strict 255-character limit or that the SPF record itself has triggered more than 10 DNS lookups. To effectively resolve this common deliverability hurdle, the most widely recommended approach is SPF flattening. This process transforms an SPF record with numerous 'include' mechanisms into a single, consolidated TXT record that explicitly lists all authorized IP addresses. By doing so, flattening significantly reduces both the overall string length and the count of DNS lookups, thereby ensuring compliance and facilitating successful SPF validation.
Key findings
- Primary Causes: The 'CharacterStringTooLong' error in SPF records stems from exceeding either the strict 255-character limit for a single DNS TXT record string or the 10-DNS lookup limit that SPF validation imposes.
- SPF Flattening as Solution: SPF flattening services are widely recommended as the primary solution to this error. They consolidate multiple 'include' statements into a single, shorter TXT record, reducing both string length and the number of DNS lookups.
- How Flattening Works: SPF flattening works by converting an SPF record's 'include' mechanisms into a direct, consolidated list of authorized IP addresses, ensuring a shorter, compliant record that avoids the lookup limit.
- Lookup Limit Connection: While the error name directly refers to string length, it is frequently a symptom of exceeding the 10-DNS lookup limit, as an increasing number of lookups inherently lengthens the SPF record string.
Key considerations
- Dynamic Updates: For environments with frequently changing IP addresses, utilizing dedicated SPF flattening services like Valimail that automatically re-flatten and update the record can simplify ongoing management and prevent re-occurrence of length issues.
- Manual Consolidation: Beyond automated flattening, manually consolidating redundant 'include' statements or removing unnecessary mechanisms can further reduce record length and help stay within the character limits.
- Post-Flattening Length: Even after flattening, the resulting SPF record must still adhere to the 255-character string limit. If it remains too long, further optimization, such as reducing included IP addresses or consolidating services where possible, may be necessary.
- Service Limitations: Typical SPF flattening services primarily resolve DNS lookups to consolidate mechanisms; they do not automatically split an excessively long flattened SPF record into multiple, consecutively linked TXT records, as SPF expects a single, compliant string.
What email marketers say
14 marketer opinions
Resolving the 'CharacterStringTooLong' error in SPF records goes beyond simply flattening 'include' mechanisms into a single TXT record. While this process is fundamental for consolidating authorized IP addresses and reducing DNS lookups, the stringent 255-character limit for each string within a DNS TXT record remains a critical constraint. Effective management often requires a dual approach, combining automated SPF flattening services with diligent manual auditing. This ensures that records stay concise, eliminating redundant entries and confirming that the final, consolidated record adheres to all technical specifications for reliable email deliverability.
Key opinions
- Strict String Limit: The fundamental DNS TXT record constraint of 255 characters applies to each string within the record, meaning a single SPF record must fit within this limit, even after flattening.
- Specialized Tool Behaviors: Certain SPF flattening tools, such as autospf.com, primarily convert 'include' mechanisms into IPv4 entries but may not automatically ensure the resulting flattened record adheres to the 255-character string limit.
- SPF's Single Record Expectation: Despite general DNS TXT record capabilities, the SPF standard mandates that its content resides within a single logical TXT record string, preventing it from being effectively split into multiple, consecutive TXT records.
Key considerations
- Proactive Record Auditing: Regularly audit your SPF record to identify and remove any outdated, unnecessary, or duplicate 'include' mechanisms, which contributes to overall record length.
- Consolidate Vendor Includes: Strategically consolidate multiple 'include' statements from the same email service provider or vendor where a single entry can cover all necessary IP ranges, reducing the overall string length.
- Alternative DNS Approaches: In rare, complex cases, consider advanced DNS strategies like using an intermediate CNAME record to point to a shorter TXT record, though this is less common than direct SPF flattening services.
- Thorough Post-Flattening Validation: Always perform a final validation of your SPF record after flattening or manual adjustments to confirm it successfully meets both the 255-character string limit and the 10-DNS lookup rule.
Marketer view
Marketer from Email Geeks explains that a DNS TXT record has a strict maximum length of 255 characters. He notes that the user's provided SPF record exceeds this limit, necessitating that it be split into multiple consecutive TXT records within the same (sub)domain DNS records.
30 Jan 2025 - Email Geeks
Marketer view
Marketer from Email Geeks explains that typical SPF flattening services perform DNS lookups to resolve includes but do not automatically create the multiple, appropriately sized TXT records required to adhere to DNS TXT record length limits.
5 Jul 2022 - Email Geeks
What the experts say
1 expert opinions
While SPF flattening is effective for reducing DNS lookups and initial record length, the 'CharacterStringTooLong' error can still occur if the final, consolidated record surpasses the 255-character limit. Expert analysis confirms that this specific error, even post-flattening, points to an overly verbose record. The key to resolving this persistent issue lies in a strategic reduction of the record's content, ensuring conciseness within DNS constraints by potentially trimming included IP addresses or mechanisms.
Key opinions
- Character Limit Always Applies: Even after applying SPF flattening to resolve the 10-DNS lookup limit, the fundamental 255-character string limit for a DNS TXT record remains a strict constraint that must be adhered to.
- Flattening's Scope: While SPF flattening effectively addresses DNS lookup issues, it does not automatically guarantee that the resulting consolidated record will fit within the 255-character limit, potentially still leading to 'CharacterStringTooLong' errors.
- Content Conciseness Needed: The primary resolution for a 'CharacterStringTooLong' error, even with a flattened SPF record, lies in making the record's content concise enough to stay within DNS character limitations, often requiring a reduction of included data.
Key considerations
- Minimize IP Ranges: Review your SPF record and identify opportunities to reduce the number of individual IP addresses or CIDR blocks included, especially if certain ranges are no longer in use or can be combined.
- Optimize Mechanisms: Carefully assess each SPF mechanism (e.g., 'include', 'a', 'mx', 'ptr') to determine if all are strictly necessary. Removing redundant or unused mechanisms can significantly shorten the record.
- Prioritize Brevity: The overarching goal is to make the SPF record as concise as possible while accurately listing all authorized sending sources. This requires a focused approach to eliminate any unnecessary characters or entries.
Expert view
Expert from Spam Resource explains that SPF records are typically limited to 255 characters. While SPF flattening helps address the 10-DNS lookup limit, if the resulting flattened record exceeds this character limit, it can lead to errors like 'CharacterStringTooLong'. The underlying resolution for such an error, even with a flattened record, is to ensure the content is concise enough to stay within DNS character constraints, potentially requiring a reduction of included IP addresses or mechanisms.
22 Dec 2023 - Spam Resource
What the documentation says
4 technical articles
When encountering the 'CharacterStringTooLong' error during SPF record management, major email and hosting providers uniformly point to two underlying causes: exceeding the 255-character limit for a DNS TXT record or surpassing the SPF 10-DNS lookup limit. To effectively mitigate this, the consensus among these experts is to implement SPF flattening. This process, whether through a specialized third-party service or by careful manual consolidation of 'include' mechanisms, transforms complex SPF records into a single, shorter string of authorized IP addresses. This strategy reduces both the character count and the number of required DNS lookups, thereby ensuring the SPF record remains compliant and functional for optimal email deliverability.
Key findings
- Dual Limit Problem: The 'CharacterStringTooLong' error is typically a symptom of exceeding either the strict 255-character limit for a DNS TXT record or the SPF 10-DNS lookup limit, as multiple lookups inherently lengthen the record.
- Universal Recommendation: Leading providers such as Google Workspace, Microsoft, Cloudflare, and Glesys consistently advise using SPF flattening services or consolidating 'include' mechanisms to resolve length and lookup issues.
- Flattening Mechanism: SPF flattening works by converting numerous 'include' mechanisms into a single, concise record of authorized IP addresses, effectively reducing the overall string length and the number of DNS queries.
Key considerations
- Leverage Third-Party Tools: Utilize reputable third-party SPF flattening services or look for consolidated SPF records provided by your primary email vendor to streamline complex records into a single, compliant string.
- Prioritize Consolidation: Actively consolidate multiple 'include' mechanisms from the same or different vendors into a single, shorter entry whenever possible to reduce both the character count and the number of DNS lookups.
- Verify Post-Flattening: Always validate your SPF record after any consolidation or flattening process to ensure it adheres to both the 255-character string limit and the 10-DNS lookup limit, preventing further deliverability issues.
Technical article
Documentation from Google Workspace Admin Help explains that the SPF record has a 255-character limit and suggests using a third-party service to flatten records or consolidating includes to resolve 'CharacterStringTooLong' errors.
19 Dec 2023 - Google Workspace Admin Help
Technical article
Documentation from Microsoft Learn, specifically regarding Exchange Online Protection, highlights the SPF 10-lookup limit and implicitly points to the necessity of keeping records concise. While not directly addressing 'CharacterStringTooLong', it implies that managing includes and flattening is essential to avoid exceeding DNS lookup limits, which often correlates with string length.
29 Aug 2022 - Microsoft Learn
How to fix SPF record exceeding DNS lookup limit?
How to format SPF TXT records, add domain includes, and avoid DNS size issues?
What are the best practices for using SPF flatteners and managing SPF records?
What are the options for dealing with overstuffed SPF records exceeding DNS lookup limits?
When is SPF flattening needed and how to validate SPF records?
Why is my SPF record too long and how to manage DNS TXT record length limits?
