From: MrC (lists-postfixcappella.us)
Date: Tue Dec 12 2006 - 13:29:18 CST

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I've been successfully using techniques similar to those described in the
BACKSCATTER_README for a while now, and they are quite effective. As
mentioned in this readme, the examples are illustrative and need to be
modified per site requirements.

I've just discovered an interesting case to watch for in your header_checks
regarding forged Message-ID headers. A header_check similar to that
presented in the readme:

        /^Message-ID:.*(MYDOMAIN\.COM)/ REJECT forged Message-ID: header:
$1

can cause unexpected rejects with Outlook 2003 when the user requests a DSN
for a message.

Outlook 2003 (perhaps Outlook Express, and other versions as well) present
substantially different Message-ID headers depending upon whether or not a
DSN is requested (via Options "Request a delivery receipt for this
message").

When a DSN is not requested, Outlook 2003 inserts a header that takes a form
such as:

   Message-ID: <032601c71e1a$6a5090$0a02a8c0HOSTNAME>

where HOSTNAME is the unqualified simple hostname of the MUA's system.

However, when a DSN is requested, the Message-ID takes the form:

    Message-ID: <!&! ...very long string... ==MYDOMAIN.COM>

where MYDOMAIN.COM is the domain name part of the email address specified in
Outlook's account settings for the user. Since many user's configure their
email addresses as NAMEMYDOMAIN.COM, messages where DSN is set will trigger
the reject action stated above.

If you offer DSN to your Outlook-using clients, it might be prudent to
precede such reject patterns with an appropriate DUNNO test to avoid
rejecting Outlook's email w/DSN enabled, or bypass such rejects for your
internal users altogether.

MrC

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