[ietf-dkim] "Best Before" vs. "expiration" date

[Paul Hoffman]

At 5:04 PM -0700 4/24/06, Michael Thomas wrote:
>Paul Hoffman wrote:
>
>>At 3:32 PM -0700 4/24/06, Jim Fenton wrote:
>>More good questions. "I, the sender, want this to not be able to be 
>>validated after this date" is all well and good, but the sender's 
>>wishes go directly against the recipient's wishes, which are to 
>>have as many validated messages as possible.
>
>That's not correct. The receiver's motivation is to defend itself.

Correct.

>Validating messages
>a priori does not do that.

True, but does it hurt to do so? If a recipient validates a message 
that has "expired", what is the harm to the recipient? The advatage, 
of course, is that they are now sure where the message came from; 
this is the same as in the normal, unexpired case.

>If a sender through its own policy says "don't trust/honor/blame me
>this after this time", why should a receiver not honor that?

If that policy makes no sense for the recipient (the sender was 
responsible at time X but not at time X+1), then the recipient would 
still want to know whether the message came from the putative source.

>  That information only negatively
>reflects on the message,  so a receiver should be happy to know.

Some recipients might be, others might not care.