Sender Policy Framework

There are multiple SPF libraries available. Many mail servers support SPF natively. Most popular mail servers also have extensions or unofficial patches available.

Reference Implementations

The Perl module Mail::SPF::Query was the very first implementation of SPF and was the de facto reference implementation for quite some time. It roughly conforms to the final SPFv1 specification, however due to its long heritage (reaching back to 2003) there are some deviations. In particular, the library does not support the final processing limits and also supports a number of non-standard features, such as best-guess processing and trusted forwarder accreditation checking.

That being said, there are currently two library implementations that are known to fully conform to the final SPFv1 specification (RFC 4408):

• pyspf 2.0: A Python module, which was the first implementation fully conforming to RFC 4408.

• Mail::SPF: An object-oriented Perl module that supersedes the old Mail::SPF::Query module. It supports both SPFv1 (v=spf1) and Sender ID (spf2.0) and is very thoroughly documented.

The jspf library is currently being evaluated by the project for RFC 4408 compliance. Libspf2 has not been updated for RFC 4408 compliance, but implements processing limits at least as strict as those required by RFC 4408.

Libraries

Mail Servers that natively support SPF

Extensions and Patches for Mail Servers

Extensions for Mail Clients

Note that performing SPF checks in the mail client is problematic because it is often difficult to accurately obtain the required information from delivered messages.

Other Software that supports SPF

Please report SPF-supporting software to the spf-discuss mailing list or by contacting us directly.