How complex is the SPF spec for building an SPF checking library?
Summary
What email marketers say10Marketer opinions
Email marketer from Mailhardener explains that while the basic concept of SPF is straightforward, the 10 DNS lookup limit creates significant challenges for larger organizations or those using multiple third-party email services, needing careful management of includes and lookups to stay within the limit.
Email marketer from StackOverflow explains that SPF can be tricky to implement due to the 10 DNS lookup limit and the difficulties managing nested include statements. He also shares that debugging SPF records can be challenging.
Email marketer from ServerFault explains that SPF looks simple on the surface but has a lot of subtle complexities that make robust implementation difficult. He references the complexity of correctly handling all of the edge cases for resource limits and DNS lookup failures
Marketer from Email Geeks says SPF macros are evil.
Email marketer from Reddit explains that SPF records are limited to 10 DNS lookups and that nested lookups count towards that limit and its common to see records that break this. They suggest ensuring the record is correct using online validators.
Email marketer from AuthSMTP explains that SPF can become complex as businesses use more cloud services, each requiring inclusion in the SPF record. This increases the risk of exceeding the 10 DNS lookup limit, requiring careful management and potentially using alternative solutions like SPF flattening.
Email marketer from EasyDMARC shares that SPF record length should be under 255 characters. Exceeding this limit can cause issues. They recommend reducing the record size where possible to avoid SPF validation failures and improve deliverability.
Marketer from Email Geeks says SPF macros are one of the reasons why he never wanted to open that box and asks Steve if he will share it on github someday.
Email marketer from Word to the Wise explains that SPF records can become complex due to the limitations, specifically the 10 DNS lookup limit. This limit requires careful planning and potentially flattening of the SPF record to ensure deliverability.
Email marketer from DMARC Analyzer explains the 10 DNS lookup limit in SPF records can easily be exceeded, causing deliverability issues. They recommend using tools to analyze and optimize SPF records to stay within the limit.
What the experts say3Expert opinions
Expert from Email Geeks shares that when it's polished it'll be at <http://github.com/wttw/spf|github.com/wttw/spf>.
Expert from Email Geeks shares he spent weeks building an SPF checking library and found the SPF spec to be complex with weird corner cases, macros, and PTR records.
Expert from Word to the Wise explains that one of the biggest challenges in SPF is that it can be hard to implement and maintain correctly. It notes that the 10 DNS lookup limit is a common source of errors.
What the documentation says5Technical articles
Documentation from RFC Editor explains that the SPF specification, while seemingly simple, has several complexities related to syntax, mechanisms, modifiers, and interactions with other DNS records which can make a robust implementation challenging.
Documentation from Google Workspace Admin Help explains that common errors in SPF records, such as exceeding the DNS lookup limit or having syntax errors, can lead to SPF failing. They also share the complexity can arise from managing multiple domains and services sending email.
Documentation from Microsoft recommends limiting the number of DNS lookups within an SPF record to avoid issues. They advise using tools to check and optimize SPF records and potentially consolidating SPF records where possible.
Documentation from Valimail explains that the complexities of SPF, particularly around DNS lookups and the limitations they impose, necessitate advanced management techniques such as SPF flattening or using a dynamic SPF solution to maintain deliverability without exceeding the limits.
Documentation from KDMARC explains that a common issue with SPF records is exceeding the 10 DNS lookup limit. It says 'include' mechanisms cause nested lookups, and too many of these can cause the record to fail and explains ways to avoid this using tools.