ietf-dkim
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Re: [ietf-dkim] user level ssp

2006-09-09 12:04:21
wayne:
1) I always sign, but I also know that I send email through relays that
   will break the signature.

This is an assertion about the sender. As such, it is valid within
the context of a sender signing policy.

1) I always sign, but I also know that I send email through relays
   that will break the signature.  If you, as a receiver, reject
   legitimate email due to broken/missing signatures, it is your fault
   and I'll place the blame on you.

This is an assertion about recipient actions and their consequences.

There is a mistaken perception that that senders have control over
how recipients handle email (whether spoofed or not). A sensible
sender signing policy is limited to assertions about sender actions.

For amusement value, below is my take on some signing policies:
after the first two, everything is either redundant, invalid, or
inconsistent.

        Wietse

0 - No policy (status quo).

1 - All mail from this domain is signed (valid).

2 - Some mail from this domain is signed (equivalent to [0]).

3 - This domain sends no mail (effectively equivalent to [1]).

4 - No-one else can sign my mail (invalid, it attempts to control
    recipient behavior where the recipient is, for example, a
    mailing list, or a user at a DKIM-signing ISP who bounces an
    email message to another site).

5 - Mail from this domain is never signed (inconsistent, it implies
    that a valid signature is invalid; and invalid, as per [4]).
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