SPF Macro
Learn what SPF macros are, how they dynamically expand during SPF checks, and how DMARCeye monitors macro usage to prevent misconfigurations.
What is an SPF Macro?
SPF macros are dynamic variables used in SPF records that allow domain owners to include runtime information in SPF evaluations. They enable advanced matching logic by inserting values such as the sender’s IP, domain, or reverse DNS result during authentication. SPF macros provide flexibility for complex mail environments that rely on variable routing or multiple sending services.
Macros appear within SPF mechanisms and modifiers using the percent symbol (%) followed by a letter representing a specific type of data. For example, %{i} expands to the sender’s IP address and %{d} expands to the domain name being checked.
How SPF Macros Work
When an SPF check is performed, the receiving server replaces macros with real-time values before evaluating the SPF record. This allows the record to adapt dynamically to different senders or message contexts.
Common SPF macros include:
%{i}— Sender’s IP address%{s}— Envelope sender address%{d}— Domain being checked%{h}— HELO or EHLO domain%{l}— Local part of the sender’s address (before the @ symbol)%{r}— Receiving server’s domain name
Example SPF record using a macro:
v=spf1 include:%{d2}.spf.example.net -allHere, the macro dynamically inserts a portion of the sending domain into the included SPF record, allowing flexible policy delegation across subdomains.
Benefits and Risks of SPF Macros
SPF macros enable powerful configurations but must be used cautiously:
- They support dynamic SPF logic for multi-domain infrastructures
- They can increase DNS query complexity and risk exceeding the DNS lookup limit
- Improper macro expansion can lead to unintended IP authorization
- They may expose sensitive data if used incorrectly
SPF Macros and DMARCeye
DMARCeye detects and interprets SPF macros during record analysis to ensure accuracy and compliance. The platform identifies dynamic components that could affect lookup counts or introduce risk, alerting administrators before misconfigurations impact authentication results.
By visualizing macro behavior and DNS dependencies, DMARCeye helps organizations manage complex SPF architectures safely and effectively.
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To learn more about DMARC and DMARC-related terms, explore the DMARCeye Glossary.