Summary
SPF macros are dynamic variables embedded within an SPF record that expand into specific contextual values at the time an email is received and its SPF record is evaluated. These values can include the sender's IP address, domain, or mailbox, among others. Their primary use is to provide more detailed and informative explanations for SPF failures through the 'exp' modifier, helping with debugging and improving deliverability insights. While not essential for basic SPF setups, macros offer powerful flexibility for complex configurations, allowing a single SPF record to adapt to various sending contexts, especially beneficial for large senders and Email Service Providers. Checking their exact values often involves understanding their dynamic expansion during the receiving process, as standard lookup tools typically do not pre-expand them.
Key findings
- Dynamic Variables: SPF macros are special variables or dynamic elements within an SPF record that are designed to expand into specific values- such as the sender's IP address, domain, or mailbox- at the moment an email is received and evaluated by the mail server.
- Primary Use Case: Their primary application is within the 'exp' (explanation) modifier of an SPF record. This allows administrators to craft more informative and human-readable bounce messages for SPF failures by embedding details like the sender's domain, IP, or email address directly into the error explanation.
- Advanced Applications: Beyond error messages, SPF macros offer advanced flexibility for complex setups, including dynamic redirection in specific scenarios or enabling granular policy checking. They are particularly beneficial for large senders and Email Service Providers (ESPs) to manage diverse sending infrastructures with a single, adaptable SPF record.
- Common Macros: Frequently used SPF macros include %s (sender), %i (client IP address), %d (domain), %h (HELO domain), %l (local part), and %v (IP version). These placeholders are replaced by the relevant data from the specific email session.
Key considerations
- Macro Expansion Dynamic: SPF macros are expanded dynamically by the receiving mail server during the SPF check, drawing values directly from the email message's SMTP session parameters. This means their values are not stored on the domain itself but are generated at the time of evaluation.
- Tool Compatibility: While online DIG tools or terminal commands like 'dig domain TXT' can validate basic SPF entries, they cannot directly show SPF macro expansion. Specialized tools like Vamsoft's SPF Policy Tester are useful for comprehensive SPF lookups and compliance checks. Be aware that some tools, such as the Word to the Wise SPF tool, do not support SPF macros and may fail when encountering them.
- Increased Complexity: SPF macros, while powerful for customization and dynamic configurations, add complexity to SPF records, making them harder to parse or manage manually. They are generally not required for simple SPF setups.
What email marketers say
13 marketer opinions
SPF macros are dynamic placeholders within an SPF record, predominantly used in the exp modifier, that expand into specific email session parameters- like the sender's IP address or domain- at the moment an email is evaluated by the recipient mail server. Unlike static DNS entries, these values are not stored on the domain but are generated during the email reception process. Consequently, conventional DNS lookup tools cannot display their expanded forms, making direct checking challenging. Instead, verifying their proper function typically involves examining SPF failure bounce messages for the dynamically generated explanation.
Key opinions
- Runtime Expansion: SPF macros function by dynamically expanding into specific values during the actual email transaction, drawing information directly from the live SMTP session rather than from pre-stored domain records.
- Enhanced Error Context: Their primary utility lies in the exp (explanation) modifier, enabling more detailed and specific reasons for SPF failures to be communicated in bounce messages, which greatly assists in diagnosing deliverability issues.
- Flexible Configurations: Although not necessary for simple setups, macros provide significant flexibility for complex email environments, allowing for adaptable SPF records that can cater to diverse sending patterns.
- Common Macro Variables: Common examples of dynamic data that can be inserted include the sender's email address (%s), the client's IP address (%i), and the sending domain (%d).
Key considerations
- Limited Direct Validation: Standard DNS lookup commands or general online DIG tools are unable to show the expanded values of SPF macros because their resolution happens dynamically at the receiving server.
- Tool Compatibility Variances: While some tools, like Vamsoft's SPF Policy Tester, are helpful for overall SPF record validation, others, such as the Word to the Wise SPF tool, are known to not support SPF macros and may fail when encountering them.
- Checking Effectiveness: The most practical way to verify an SPF macro's effectiveness is to observe the content of bounce messages received for SPF failures, as these will reflect the dynamically populated explanation.
Marketer view
Email marketer from Email Geeks explains that SPF entries can be validated using online DIG tools or by running `dig domain TXT` in a *nix or MacOS terminal.
2 Feb 2022 - Email Geeks
Marketer view
Email marketer from Email Geeks clarifies that SPF macro values are taken directly from the email message, rather than being stored on the domain.
28 Jul 2023 - Email Geeks
What the experts say
2 expert opinions
SPF macros enhance deliverability by allowing a single SPF record to dynamically adapt to various sending contexts, such as different sending IP addresses or recipient domains. This capability enables recipient servers to perform more granular policy checks. Consequently, SPF macros are particularly beneficial for Email Service Providers (ESPs) and other large senders who need to manage complex email infrastructures efficiently.
Key opinions
- Dynamic Adaptability: SPF macros allow a single SPF record to dynamically produce different evaluation results based on various aspects of the email's sending context, such as the sending IP address or recipient's domain.
- Granular Policy Checking: They enable recipient servers to perform more granular and precise policy validations, leading to more accurate authentication outcomes.
- Complex Infrastructure Utility: This functionality is most commonly utilized by large senders and Email Service Providers (ESPs) to manage their diverse sending infrastructures effectively with a single, adaptable SPF record.
- Variable Insertion: Macros function by dynamically inserting variable values- like the sending IP address or recipient's domain- into the SPF record during the evaluation process.
Key considerations
- Simplified Management for Large Senders: SPF macros enable Email Service Providers and other large senders to manage complex sending infrastructures more efficiently, allowing a single SPF record to validate mail from various customer domains or IP ranges.
- Contextual Validation: Their dynamic nature ensures that SPF checks are always relevant to the specific message and its unique sending circumstances, improving the accuracy of authentication.
- Enhancing Deliverability: By providing a mechanism for adaptive policies, SPF macros significantly contribute to improved email deliverability for organizations with diverse and complex sending requirements.
Expert view
Expert from Spam Resource explains that SPF macros enable more granular policy checking by recipient servers. They work by dynamically inserting variable values, such as the sending IP address or recipient's domain, into the SPF record during evaluation. This allows a single SPF record to adapt to different sending contexts, making it particularly useful for Email Service Providers (ESPs) to manage complex sending infrastructures and improve deliverability.
9 Jun 2025 - Spam Resource
Expert view
Expert from Word to the Wise explains that SPF macros function by allowing a single SPF record to dynamically produce different evaluation results based on various aspects of the message's sending context. For example, it can allow different IP addresses for different recipients or sending domains. This functionality is most commonly utilized by large senders and ESPs, enabling them to have one SPF record that validates mail from various customer domains or IP ranges through dynamic expansion.
16 Dec 2023 - Word to the Wise
What the documentation says
4 technical articles
SPF macros serve as dynamic elements within an SPF record, predominantly utilized in the 'exp' modifier to provide precise explanations for SPF authentication failures. These values, such as the sender's IP address or domain, are not static but are expanded in real-time by the receiving mail server during the evaluation process based on SMTP session parameters. This dynamic insertion capability makes SPF records more flexible for complex email environments and greatly aids in diagnosing deliverability issues by offering context-rich information in bounce messages. While powerful, their dynamic nature means they cannot be checked via simple static DNS lookups; their effect is best observed in the generated failure explanations.
Key findings
- Dynamic Expansion: SPF macro values are dynamic, expanding at the moment an email is evaluated by the recipient server, drawing specific data from the live SMTP session parameters like the sender's IP address or domain.
- Contextual Error Messages: These macros are primarily utilized within the 'exp' modifier of an SPF record to provide human-readable, context-specific explanations for SPF authentication failures in bounce messages.
- Variable Insertion: Common macros like %s (sender), %i (client IP), %d (domain), %h (HELO domain), %l (local part), and %v (IP version) allow for the dynamic insertion of specific email-related data into the SPF record's evaluation.
- Diagnostic Aid: By enabling detailed failure explanations, SPF macros significantly help in understanding and diagnosing the root causes of email deliverability issues for senders and administrators.
Key considerations
- Verification Challenge: Direct checking of SPF macro values is not feasible through static DNS lookups, as their expansion occurs dynamically on the receiving server; verification typically involves observing bounce messages for dynamically generated explanations.
- Increased Complexity: While offering powerful customization and dynamic capabilities, SPF macros can increase the manual complexity of parsing and managing SPF records, making them harder to understand without proper tools or knowledge.
- Advanced Use Cases: Beyond their primary use in error explanations, SPF macros also provide flexibility for advanced configurations, including dynamic redirection mechanisms within SPF records.
Technical article
Documentation from RFC Editor explains that SPF macro values are dynamic elements within an SPF record's exp modifier or redirect mechanism, allowing the sender's domain, IP address, or other variables to be inserted at the time of evaluation. These macros provide flexibility in constructing bounce messages or redirecting SPF checks, for example. The document specifies how macros like %s (sender), %l (local part), %o (domain), %i (IP address), and %v (IP version) are expanded based on the SMTP session parameters.
12 Aug 2023 - RFC Editor
Technical article
Documentation from MXToolbox explains that SPF macros are used to insert dynamic information into an SPF record, primarily within the exp= modifier, which provides a human-readable explanation for SPF failures. Common macros include %s for sender, %i for client IP, %d for domain, and %h for HELO domain. They allow for highly customized error messages or for dynamic redirection in advanced configurations, though they can also make records more complex to parse manually.
5 Mar 2023 - MXToolbox
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