ietf-dkim
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Re: [ietf-dkim] On the Selector

2009-05-26 10:53:36

On May 25, 2009, at 7:14 PM, Steve Atkins wrote:


On May 25, 2009, at 5:48 PM, Franck Martin wrote:

see

http://feedbackloop.yahoo.net/
http://www.gettingemaildelivered.com/yahoo-feedback-loop-released-to-the-public

Yup, that's connected to the Returnpath feedback loop, rather than  
reputation tracking. They're allowing you to sign up for a feedback  
loop for a particular d= value and for either one specific selector  
or all selectors.

When tracking specific issues it may well be useful to get FBL  
reports for just one specific user of a DKIM identity, and being  
able to key on selector seems a good enough way to do that, if a bit  
of a hack.  It's not something I'd expect anyone to use normally,  
though.


The s= value represents a valid choice for separating feedback  
reports.  The domain may use keys for different purposes, where the s=  
value could be used to establish different priorities.

While d= represents the first element that should be checked for  
reputation, either the i=,  or the author address when the i= is not  
available, could be used as an intra-domain identifier.  Provided the  
domain only has a few bad actors (normally less than one percent for  
well managed domains) a secondary check point would allow a means to  
exclude intra-domain bad actors that might otherwise replay their DKIM  
messages well beyond the normal rate-limits that a provider may have  
established.  The only other alternative strategy would be register  
the the path of the DKIM signatures, but then this would not be as  
robust.  As IP address reputation becomes more complete, the remaining  
avenue for spammers is to utilize provider's main servers.  There are  
enough user systems compromised, that normal rating limiting will not  
be affective.  With respect to DKIM, rate limiting is not effective  
against replay abuse.

Checking the d= value's reputation should provide a high cache hit  
rate.  If this represents a bad-actor, which is likely the case, then  
no other query is required.   When the d= value's reputation indicates  
there is no intra-domain problems, then again no other query is  
required.  However, when intra-domain problems exist, use of the i=  
value or that of the author address converted to a hash could  
represent the next query made.

-Doug
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