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Re: [ietf-dkim] x= lets senders expire responsibility

2006-04-13 10:09:35

On Apr 13, 2006, at 9:43 AM, Hector Santos wrote:

That basically means that x= must be used if there is a planned event
for selector removal within 7 days.

When the transport includes IMAP and POP, this 7 day advice is far
too short of a period to ensure verification.

Agreed. This SWAG must be from the recommended SMTP retry limits:

| RFC 2821:
| 4.5.4.1 Sending Strategy
|
|  ...
|
| Retries continue until the message is transmitted or the sender gives
|  up; the give-up time generally needs to be at least 4-5 days.  The
|  parameters to the retry algorithm MUST be configurable.


But for the time-shifted application, if the message reception time
(Received: header) is used, then it shouldn't matter.

When verification occurs at the MUA, the key must remain available _beyond_ the SMTP transport period. Removing keys prior to verification impacts assurances being sought with DKIM. DKIM protects messages through more than just the SMTP transport, and is one reason given for excluding the envelope.

-Doug





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