Introduction
SPF (Sender Policy Framework) is a well-known standard in email security. However, the limitations that come with it are often overlooked, specifically the 10 DNS Lookup limit and the lesser-known Void Lookup limit. This blog post reveals these limitations, their implications, and how to navigate them effectively.
The 10 DNS Lookup Limit for SPF Records
Why It Matters
Your SPF limit of 10 DNS Lookups can significantly impact email authentication. Each new ‘mechanism’ added to your SPF record necessitates a new DNS lookup. The more third-party vendors you rely on for sending emails, the more mechanisms you’ll need, thereby increasing your DNS lookups.
The Consequences
Exceeding the 10 DNS Lookup limit results in a ‘PermError SPF permanent error: too many DNS lookups.’ This invalidates your SPF record, leading to email delivery issues you might not even know about.
The Reason Behind the Limit
The 10 DNS Lookup limit is not arbitrary; it’s designed to mitigate Denial-of-Service attacks, as specified under RFC 7208. However, this safeguard can sometimes do more harm than good, making solutions like SPF flattening essential.
SPF Void Lookups: The Lesser-Known Limit
What Is It?
As specified by RFC 7208 (section 11.1), the SPF void lookup limit is currently set at 2. Unlike the 10 DNS lookup limit, SPF void lookups occur when a DNS lookup returns a void or null response during an SPF check.
Why It Happens
This usually occurs when your SPF record contains an ‘include’ mechanism that refers to an erroneous or malicious domain or IP address. Exceeding this limit also results in an SPF PermError, affecting email delivery.
How to Mitigate SPF Limitations
SPF Flattening
SPF flattening shortens your SPF record to stay within the 10 DNS lookup limit. Automated SPF flattening tools can help you maintain your record length and stay updated with any IP address changes.
Why Manual SPF Record Flattening Isn’t Enough
SPF records need constant updating, especially if you’re using multiple third-party vendors for email sending. Manual updates are tedious and prone to errors, leading to SPF permerrors or temperrors.
Conclusion
Understanding the limitations of SPF is crucial for adequate email security and deliverability. While the 10 DNS lookup limit is well-known, the void lookup limit is often overlooked. Being aware of both and using automated tools for SPF flattening can save you from unnecessary headaches and potential security risks.
By understanding these limits and navigating them, you can ensure that your email security protocols are compliant and effective.
If you have questions regarding email deliverability and automation, comment below and I will reply.
Cheers,
Fabrício
