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Sender Policy Framework


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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.


libspfCJames Couzens, Sean ComeauJames Couzens
libspf2CShevek, Wayne Schlittsee website
RMSPFC (Windows)Roger MoserRoger Moser
Mail::SPFPerlJulian Mehnle, ShevekJulian Mehnle
pyspfPythonStuart Gathman, Terence Waysee Python Cheese Shop
jSPFJavaStefano Bagnara, Norman Maurersee website

Mail Servers that natively support SPF

ArGoSoft Mail Server ProArGo Software Design
Communigate ProStalker
Couriersee website
Exim >=4.52The Exim Project
Gordano Message SuiteGordano
Hexamail Server and related productsHexamail
IMail Ver. 8.22 and higherIpswitch
Kerio MailServerKerio
MDaemonAlt-N Technologies
Merak Mail ServerIceWarp
WIN ServerSantronics Software

Extensions and Patches for Mail Servers

NameMail ServerAuthor(s)Contact
Courier::Filter SPF ModuleCourierJulian MehnleJulian Mehnle
Courier Python FilterCourierGordon MessmerGordon Messmer
exiscan ACLExim <4.52Tom KistnerTom Kistner
Exim patchExim 4.43nslmnslm
MEFilterMailEnableMartyn KeenMartyn Keen
libspf2 Postfix policydPostfixShevek, Wayne Schlittsee website
postfix-policyd-spf-perlPostfixMeng Weng Wongspf-discuss
tumgreyspfPostfixSean Reifschneider, tummy.comsee website
Modular Python Postfix Policy ServerPostfixPetr Vokacsee website
Postfix Policy Server v2PostfixMichael Langsee website
ACL Policy DaemonPostfixThe Gna! Projectsee website
Whitelister OCAML Policy DaemonPostfixPierre HabouzitPierre Habouzit
libspf2 Postfix PatchPostfixDean StrikDean Strik
libspf2 >= 1.2.0 patchPostfixNigel KukardNigel Kukard
Qmail PatchQmail 1.03Christophe SaoutChristophe Saout
libspf Qmail PatchQmailJames Couzens, Sean ComeauJames Couzens
Plugin includedqpsmtpdAsk Bjørn Hansensee website
libspf/libspf2 spfmilterSendmailJef PoskanzerJef Poskanzer
smf-spf MilterSendmailEugene KurmaninEugene Kurmanin
spf-milter (upstream, RPM, on site)SendmailMark KramerMark Kramer
Python MilterSendmailJim Niemira, Stuart D. Gathmansee website
milter-spiffSendmailAnthony Howesee website
Milter GreylistSendmailEmmanuel Dreyfus et al.see website
libspf Sendmail PatchSendmailJames Couzens, Sean ComeauJames Couzens
Policy Patrol Spam FilterExchange,
Lotus Domino
Red Earth Softwaresee website
SPF Event SinkIIS SMTP Server,
Exchange 2000
Johan StrandJohan Strand
MailEssentialsAnti-Spam Filter Plugin for
IIS SMTP Server, Exchange
GFI Softwaresee website
Sunbelt Messaging NinjaExchange 2000/03Sunbelt Softwaresee website

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.

NameMail ClientAuthor(s)Contact
Thunderbird Extension for Sender VerificationThunderbirdJoshua Tauberersee website

Other Software that supports SPF

Aloaha SPAM RejectorAnti-Spam SMTP ProxyAloaha Software
ASSPAnti-Spam SMTP ProxyThe ASSP project
CanItAnti-Spam Filter Plugin for SendmailRoaring Penguin Software
GWGuardianNovell GroupWise spam protectionMessaging Architects
IronPortAnti-Spam FiltersIronPort
LeonCorporate Anti-Spam ServerUniwares
Mail AvengerAnti-Spam SMTP ProxyDavid Mazières
Memova Anti-AbuseAnti-Abuse ApplianceCritical Path
PowerDNSDNS ServerPowerDNS
SpamAssassinAnti-Spam ScannerApache Software Foundation (ASF)
Spug SpamProcmail C/R PluginMike Muller
Various productsE-mail Security SoftwareSymantec
XWallAnti-Spam SMTP ProxyDataEnter
Shielded MailMail Filtering Relay ServiceSoftPark Technologies

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