Here are the relevant parts from a new internet-draft I'm preparing. The
working form of the document itself can be found at
http://www.nisto.com/listspec/#DOCUMENTS
Please address all follow up to the list-header mailing list
<[EMAIL PROTECTED]> <http://www.nisto.com/listspec/mail/>,
or to me privately. Thanks.
The List-Probe Message Header Field for
Identifying Mail List Probe Messages
Abstract
This document defines the message header field "List-Probe"
to be used in consistently identifying mail list probe messages.
1. Introduction
Many MTAs (mail transfer agents - mail servers) in use today do not
provide adequate details when failing to transfer mail messages. In
particular, when email is automatically forwarded from a recipient
address to a second address that is 'bouncing' incoming mail, the
error response messages may not properly including the original
(forwarding) recipient address.
To help deal with this problem, many mailing list managers have taken
to sending out individualized "probe" messages. The probes include
enough identifying information - even if the original recipient
address is not included in the error response - that the forwarding
address can be properly identified.
The drawback to this approach is that valid recipients will receive
the probe messages in their mail - an unfortunate waste of time and
resources.
This document defines a message header field, List-Probe, which will
allow MUAs (mail user agents - email clients) to identify and
automatically discard probe messages so the user does not have to be
involved in the process. If a probe message is received by a MUA,
the recipient address is valid, so the probe does not need to be
responded to (and can safely be discarded) since probes are only
seeking error responses.
2. The List-Probe Header Field
The List-Probe message header field MUST contain a single RFC822
format recipient address. The field MAY also contain round-bracket
enclosed comments.
For example, a probe message for the address [EMAIL PROTECTED] might
look like:
List-Probe: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
From: [EMAIL PROTECTED]
Errors-To: [EMAIL PROTECTED]
Subject: Probe message - Please ignore
We are checking for invalid email addresses.
Since you have received this message, your email is valid.
Please discard this message - DO NOT REPLY.
Our appologies for the interruption.
3. Security Considerations
Since the originating system is responsible for introducing the
List-Probe field into the message, with the expectation that valid
recipients will discard the message, it is expected that no unwanted
message discarding will occur.
There is a danger that senders of unwanted bulk email could make use
of the List-Probe field in validating recipient addresses. To provide
users with the option to avoid this, MTAs MUST provide an option to
ignore the List-Probe field (not deleting the messages), allowing the
user to see the probe messages. In the case of ignoring the
List-Probe field, the MTA MAY hilite the message in some manner to
alert the user that it is a probe message.
Mail list processors SHOULD NOT allow user-originated List-Probe
fields to pass through to their lists, lest they confuse the user and
have the potential to create security problems.
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