Re: [EXIM] sender verify snafu

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Author: Philip Hazel
Date:  
To: mark david mcCreary
CC: exim-users
Subject: Re: [EXIM] sender verify snafu
On Thu, 30 Jul 1998, mark david mcCreary wrote:

> Date: Thu, 30 Jul 1998 23:54:17 +0100


I make that time equivalent to 22:54:17 UTC on 30 Jul, but in the log
you are quoting, a time of 31 Jul 1998 04:08:58 +0000 is quoted. Am I
missing something, or is somebody's clock wrong?

> I am using the sender_verify options with fairly good success, at keeping
> out spam and other crap from email that does not properly identify itself.
>
> However, I have one or two cases where bounces are being returned, and my
> machine rejects them. Their machines are quite persistent though, and keep
> trying over and over.


It is an unfortunate fact that a number of SMTP clients, in violation of
the RFCs, do not treat a permanent error code that is given after the
DATA portion of the transaction as a permanent error. Consequently they
keep resending the message.

> ------------------------------------------------------------------------------
> 1998-07-31 04:09:00 0z26Uz-0003uT-00 rejected from (lhl.gundluth.org)
> [204.69.145.17]: no valid sender in message headers: return path is <>
> Recipients: pjalert-admin@???
> P Received: from (lhl.gundluth.org) [204.69.145.17]
>    by dispatch.mail-list.com with smtp (Exim 1.82 #7)
>    id 0z26Uz-0003uT-00; Fri, 31 Jul 1998 04:08:58 +0000
>   X-Nvlenv-01Date-Posted: 29-Jul-1998 22:50:52 -0500; at lhlnwc1.gundluth
>   Mime-Version: 1.0
>   Content-Type: multipart/mixed;
>        boundary="PartBoundary_Wed_Jul_29_22:51:30__3897960"
>   Date: 29 Jul 98 22:50:52 CDT
> T To: pjalert-admin@???
> F From: mailer-daemon@???
> I Message-Id: <"9FEABF3581A2357C@???"@-SMF->
>   Subject: Returned mail: Non delivery of message.
> ------------------------------------------------------------------------------


The error here is not a consequence of sender_verify, but of
headers_sender_verify or headers_sender_verify_errmsg. That's why it
says "no valid sender in message headers". Because it is the result of a
check of the content of the message, it can only be sent as an error
response to the DATA portion.

> First of all, I would have kinda expected <> to be a valid envelope sender
> address, for these purposes.


It is. The problem is with the header line

From: mailer-daemon@???

If you try to route to that address, you get

taurus$ exim -bt mailer-daemon@???
mailer-daemon@??? is undeliverable:
all relevant MX records point to non-existent hosts:
it appear that the DNS operator for this domain has installed an invalid MX
record with an IP address instead of a domain name on the right hand side

and indeed, if you look up the MX records, you find

MAIL.GUNDLUTH.ORG.      86400   MX      0 204.69.145.17.
MAIL.GUNDLUTH.ORG.      86400   MX      20 204.69.147.17.
MAIL.GUNDLUTH.ORG.      86400   MX      10 204.69.149.17.


The DNS manager for that zone has screwed up, and made a very common
error. I will attempt to send a message to that effect.

> Second, I would have thought that the sender_verify_fixup would have
> allowed a valid From Header, which based on the log, seems to be
> mailer-daemon@???.


Not relevant. This isn't concerned with sender_verify.

> Third, in reading chapter 40.2, it seems that this persistent domain should
> be stuck in some sort of database, and if repeated tries are made, then a
> 550 return code is sent back. That may be happening, although this
> particular machine is trying to return this bounce every minute or so.


This applies only to sender_verify, and this isn't a case of
sender_verify failing. Retrying every minute indicates a seriously
stupid MTA.

-- 
Philip Hazel            University of Cambridge Computing Service,
ph10@???      Cambridge, England. Phone: +44 1223 334714.



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