Subject: Using Sender-ID as an inefficient CSV

From: Tony Finch <[email-masked]>
Date: Mon, 16 Aug 2004 08:57:59 +0100

Some observations about Sender-ID:

(1) It screws up forwarding, which is very popular at sites like mine.

(2) Although it appears to authenticate email addresses, it actually
authenticates domains (since the local part is ignored).

(3) Although it appears to authenticate domains, it actually authenticates
MTAs (since anyone authorized to use an MTA can send email "from" any
domain which uses that MTA).

The easiest way to fix a site to avoid complaints from users resulting
from Sender-ID rejections is to add before the usual Received: line at the
start of the message
	Resent-Sender: [email-masked]

Of course outgoing.mail.relay is exactly what CSV authenticates.

Tony.
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