On Tue, 21 Nov 2006, George Hitz wrote:
I found a white paper on SES protocol (dated 2004) so will
try to understand that concept and see if it applies in my
situation. I don't think it does.
Here is how MAIL FROM signing works. This example uses SRS in signing
mode.
Yesterday I sent an email with
MAIL FROM: <stuart(_at_)bmsi(_dot_)com>
My pysrs software changed that to:
MAIL FROM: <SRS0=809Ap=FA==stuart(_at_)bmsi(_dot_)com>
Now, should there be a delivery problem, the MTA detecting the problem
should send a DSN with
MAIL FROM: <>
RCPT TO: <SRS0=809Ap=FA==stuart(_at_)bmsi(_dot_)com>
When pysrs sees a DSN to a signed address, and the cookie matches a current
secret, the RCPT TO is reversed back to the original:
MAIL FROM: <>
RCPT TO: <stuart(_at_)bmsi(_dot_)com>
and it gets delivered.
DSNs to unsigned RCPT TO, or cookie doesn't match (or is stale), are
rejected. This gets rid of all the bounced forgeries and forged bounces.
That is all great. The big weakness, however, is that too many IDIOTS
write MTA software and don't actually send DSNs. They send auto-responses.
They will even send an auto-response to a DSN! I've heuristically
identified some conditions which make me change the MAIL FROM to <>:
1. MAIL FROM is postmaster(_at_)(_dot_)(_dot_)(_dot_)
2. From: header field is postmaster(_at_)(_dot_)(_dot_)(_dot_)
3. Content-type: header field has report-type=delivery-status
The problem with the last two, is that it is too late to reject before DATA.
The problem with the first two that postmaster *should* be able to send
email. Sigh.
-
Stuart D. Gathman <stuart(_at_)bmsi(_dot_)com>
Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154
"Confutatis maledictis, flammis acribus addictis" - background song for
a Microsoft sponsored "Where do you want to go from here?" commercial.
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