-----Original Message-----
From: asrg-admin(_at_)ietf(_dot_)org [mailto:asrg-admin(_at_)ietf(_dot_)org]
On
Behalf Of Yakov Shafranovich
At 08:01 PM 7/3/2003 -0600, Selby Hatch wrote:
Yakov Shafranovich wrote:
....
In the consent model we have a SENDER and RECEIVER of email that
communicate with each other. The messages between the SENDER and the
RECEIVER are processed by MUAs and transferred by MTAs. The
RECEIVER can
express his CONSENT POLICY to his MUA and MTA, which will
enforce it for
incoming messages. This policy
References to this policy . . . (not the entire policy)
The whole policy cannot be shared with the sender since it will simply
allow the sender to guess what kind of messages can go through
UNLESS the
policy relies on trusted third parties such as CAs for consent tokens.
What if the policy included hinting such that a new inbound message
which does not satisfy the policy is rejected, but the rejection
includes a recommended alternative (a hint) for satisfying the policy,
or indicates precisely what part of the policy failed. This would allow
new anonymous senders to gain access via some means selected by the
receiver without exposing the receiver's policy to the sender.
For instance:
IRRQ (Intelligent Retry Request) does this by making a small alteration
to the SMTP protocol by rejecting the message with a temporary failure
(indicating that the policy was not satisfied) and providing a
one-time-password in the form of an email address that the sender may
include if they are legitimate. This is a variation on "greylisting".
==> RCPT TO: <original-recipient(_at_)example(_dot_)com>
<== Temporary failure, try again with
<randomfoo1bar2xyzq(_at_)example(_dot_)com>
.... Sender waits a nominal period of time for the retry ....
===> RCPT TO: <foo1bar2xyzq(_at_)example(_dot_)com>
<=== OK
===> RCPT TO: <original-recipient(_at_)example(_dot_)com>
<=== OK
This might be employed where the policy is for new unkown senders to
implement IRRQ. Other policies and response mechanisms could be applied
depending upon what is available and appropriate as selected by the end
user and the provider of the RECEIVER. This IRRQ example is just a "for
instance".
All forms of this kind of system ultimately become some kind of
challenge-response mechanism where the initial rejection is essentially
a challenge, and the appropriate follow up is essentially a response.
_M
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