RE: Replay attacks and ISP business models

["Hallam-Baker, Phillip" <pbaker@xxxxxxxxxxxx>]

> [mailto:owner-ietf-mailsig@xxxxxxxxxxxx] On Behalf Of Douglas Otis

> If replay does become a problem, then what is the response?  
> Should large domains then issue user-keys to everyone? 

There is actually little difference in per-user keys and signing the
sender field.

Per user keys only make a difference if they are individually
controlled.

 
>  The value of this acceptance is reduced when a signature 
> must also be checked against a third-party clearing house to 
> decide whether this represents a message being abusively replayed.

Are you arguing that the third party clearing house protocol is
absolutely essential for DKIM to have any value at all?