SPF plugin

This plugin implements RFC 4408 Sender Policy Framework (SPF) See the Wikipedia article on SPF for details.

By default this plugin with only add trace Received-SPF headers to a message. To make it reject mail then you will need to enable the relevant options below. [deny]helo_fail and [deny]mfrom_fail are the closest match for the intent of SPF but you will need to whitelist any hosts forwarding mail from another domain whilst preserving the original return-path.

Configuration

This plugin uses spf.ini for configuration and the following options are available:

[relay]
context=sender   (default: sender)

On connections with relaying privileges (MSA or mail relay), it is often desirable to evaluate SPF from the context of Haraka's public IP(s), in the same fashion the next mail server will evaluate it when we send to them. In that use case, Haraka should use context=myself.

* context=sender    evaluate SPF based on the sender (connection.remote.ip)
* context=myself    evaluate SPF based on Haraka's public IP

The rest of the optional settings (disabled by default) permit deferring or denying mail from senders whose SPF fails the checks.

Additional settings allow you to control the small things (defaults are shown):

; The lookup timeout, in seconds. Better set it to something much lower than this.
lookup_timeout = 29

; bypass hosts that match these conditions
[skip]
; hosts that relay through us
relaying = false
; hosts that are SMTP AUTH'ed
auth = false

There's a special setting that would allow the plugin to emit a funny explanation text on SPF DENY, essentially meant to be visible to end-users that will receive the bounce. The text is http://www.openspf.org/Why?s=${scope}&id=${sender_id}&ip=${connection.remote.ip} and is enabled by:

[deny]
openspf_text = true

; in case you DENY on failing SPF on hosts that are relaying (but why?)
[deny_relay]
openspf_text = true

Things to Know

• Most senders do not publish SPF records for their mail server hostname, which means that the SPF HELO test rarely passes. During observation in 2014, more spam senders have valid SPF HELO than ham senders. If you expect very little from SPF HELO validation, you might still be disappointed.
• Enabling error deferrals will cause excessive delays and perhaps bounced mail for senders with broken DNS. Enable this only if you are willing to delay and sometimes lose valid mail.
• Broken SPF records by valid senders are common. Keep that in mind when considering denial of SPF error results. If you deny on error, budget time for instructing senders on how to correct their SPF records so they can email you.
• The only deny option most sites should consider is mfrom_fail. That will reject messages that explicitely fail SPF tests. SPF failures have a high correlation with spam. However, up to 10% of ham transits forwarders and/or email lists which frequently break SPF. SPF results are best used as inputs to other plugins such as DMARC, spamassassin, and karma.
• Heed well the implications of SPF, as described in RFC 4408

[defer]
helo_temperror
mfrom_temperror

[deny]
helo_none
helo_softfail
helo_fail
helo_permerror

mfrom_none
mfrom_softfail
mfrom_fail
mfrom_permerror

openspf_text

; SPF settings used when connection.relaying=true
[defer_relay]
helo_temperror
mfrom_temperror

[deny_relay]
helo_none
helo_softfail
helo_fail
helo_permerror

mfrom_none
mfrom_softfail
mfrom_fail
mfrom_permerror

openspf_text

Testing

This plugin also provides a command-line test tool that can be used to debug SPF issues or to check results.

To check the SPF record for a domain:

# spf --ip 1.2.3.4 --domain fsl.com
ip=1.2.3.4 helo="" domain="fsl.com" result=Fail

To check the SPF record for a HELO/EHLO name:

# spf --ip 1.2.3.4 --helo foo.bar.com
ip=1.2.3.4 helo="foo.bar.com" domain="" result=None

You can add --debug to the option arguments to see a full trace of the SPF processing.

SPF Resource Record Type

Node does not support the SPF DNS Resource Record type. Only TXT records are checked.

This is a non-issue as < 1% (as of 2014) of SPF records use the SPF RR type. Due to lack of adoption, the next SPF revision will like likely deprecate the SPF RR type.