[ietf-dkim] DKIM signature can mean it's safe to generate bounce?

[Douglas Otis]

On Jul 6, 2007, at 5:36 PM, Michael Thomas wrote:

> Steve Atkins wrote:
>>
>> If the mail is sent by dick at earthlink.net (or a virus on their  
>> machine), with an envelope from address of jane at earthlink.net out  
>> through the DKIM stamping earthlink smarthost and you generate a  
>> bounce, that bounce will go to Jane.
>
> Sure, but at least it's reduced to an intra-domain problem which  
> earthlink has the capacity to remedy.

Unless Earthlink uses per-user keys, Earthlink will need to wait for  
the signature to expire.  Even the costly step of invalidating per- 
user-keys is not likely to be effective at dealing with a replay   
problem.  Messages can come from any number of compromised systems  
within their network.  Nothing within DKIM offers Earthlink the  
"capacity" to safely deal with a replay problem.

TPA-SSP offers a means for recipients of Earthlink messages to better  
cope with a possible replay problem.  When a domain signing a message  
has been "authorized" as "strict", the "authorized" domain should  
also normally administer the SMTP client transmitting the message to  
a public server.  By limiting the cases of possible replay abuse,  
this containment provides the capacity to better deal with possible  
replay problem without resorting to per-user keys.

-Doug