[RCU] [DMARC-Fail] Continuing DKIM problems with RCM servers?

Steve Wilson steve+roundcube-users at swsystem.co.uk
Mon May 10 04:06:45 CEST 2021

As this list adds/ensures "[RCU]" is in the subject, that's at least one 
component that's changing. It also appends the mailing list signature as 
a footer to the body which changes that too.

I should have dkim on my mails, so I'm curious now how mine's configured 
too as I don't see failures with various lists.


On 10/05/2021 01:47, rc at passwall.com wrote:
> From the DKIM header assumed added by your MTA:
> "
> DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed;
>  d=pricom.com.au; s=phr1; x=1620760128; h=MIME-Version:
>  Content-Type:Content-Transfer-Encoding:Date:From:To:Cc:Subject:
>  Reply-To:In-Reply-To:References:User-Agent:Message-ID; bh=FmYpFg
>  8n5qzZwGVS9g1ntm5elRA=; b=oRoLjUkhqBD4I7O17UaQEiwoku0KRuVy5/Ghjb
>  2HhS4HIQMoPOK7JsinkxKUuK4Ux0XJlJAukaD7uSG61aCadR6kRXurcAtSv8kY79
>  w6q2PAf/JPofvR1xVpvN4E1MGqM80s9G6fpvHCdzV0fJKRseoFpZZhkSlctcXPFh
>  95i5E=
> "
> This implies that your MTA DKIM signing includes all of these in the 
> computer DKIM value for your messages:
> MIME-Version
> Content-Type
> Content-Transfer-Encoding
> Date
> From
> To
> Cc
> Subject
> Reply-To
> In-Reply-To
> References
> User-Agent
> Message-ID
> If only this list is showing DKIM validation failure while sending to 
> you test email say gmail show DKIM validation as working, you should 
> have all the information you need in order to find the cause.
>  1) The case where it always breaks.
>  2) The case where it always succeeds.
>  3) The same test which can exercise both.
>  4) Access to compare the results to look for differences
> Email a message to the list from the troubled DKIM signing service, 
> and CC your gmail account which shows DKIM signing works.
> To be the most kind to list members, make your test be something that 
> is on-topic to the list, so it isn't a junk message sent to all list 
> members, distributing a cost of reading and deleted or just deleting a 
> test message among many people. (You could imagine the kind of wasted 
> time if everyone on the list tested DKIM with test messages of no 
> value to any other members.)
> Complete a character-by-character comparison of each of the items your 
> MTA uses to compute your DKIM sig between the message to the list, and 
> the copy of the same message you CC-ed to your gmail account. (Subject 
> is a common place for a message to get marked-up like with adding 
> [RCU] to a subject. This is often resolved by adding another DKIM sig 
> which includes those changes, and get used instead of later DKIM.
> If every single character (including whitespace tabs vs space, \r vs 
> \n, etc), extra whitespaces, especially in between strings without 
> previous spaces and alphabetic characters match for headers specified 
> in DKIM header for sigs are exactly the same, then 2 sore-spots for 
> you to investigate which are common sources of problems:
>  1) The separation between "headers" and "body" : some services will 
> violate an *implied* process for adding headers to e-mail messages and 
> "add them at the bottom" between the headers / body separation, which 
> can sometimes cause problems with dkim validation. (IIRC, the mail RFC 
> only says header ^Received.* lines must be added at top top in order 
> they are added, but I don't recall comment for other headers mentioned 
> in email RFC being required to always be added only to the top. (Other 
> RFC for other e-mail headers can indicate only adding to top in 
> chronological order.) Most of the time, MTA and milters will do the 
> commonly accepted thing and add only to the top, but some do not, and 
> can break the method used to separate headers from body and break DKIM 
> eval. It can happen with the last header adding an extra '\n' or 
> adding a '\r' or other causes.
>  2) Footers added by lists (and extra characters including 
> whitespaces) can also break DKIM evaluation of the body, consider 
> copying the broken message to a text file and run your favorite DKIM 
> validation tool against the message with the bad DKIM check, removing 
> items or revising items not included in the gmail received message or 
> change on list-message compared to gmail message.
> The above can usually help a mail admin identify the causes email from 
> for *their* failing DKIM checks on lists with DKIM checks from other 
> users are fine. There are other cases for causing problems, but the 
> above is usually enough to identify most causes. If the above is not 
> enough, consider possible multibyte charset homograph replacement, and 
> check for those.
> Other tests can be done if you can control the attributes that DKIM 
> uses to generate a sig, but that "trial and error" approach to 
> diagnosing problems is usually considered very bad for mailing lists 
> members.
> Next, if you are using a 4k key for DKIM signing, that can cause 
> problems with some older dkim validation tools. 2k seems well supported.
> Last, consider changing your dkim hashing ALG from sha1 to one of the 
> sha2 class of hashing (sha2 or sha256 (a=rsa-sha256;), etc.) (As of 
> the writing of this message, sha1 has been phased out of many crypto 
> systems for hashing. In the future, sha2 classes will probably be 
> phased out and not be suggested.)
> HTH you or someone else,
> Good luck!
> On 2021-05-09 03:34, Philip Rhoades wrote:
>> People,
>> My mail server guru sent me the response below when I asked him about
>> getting error messages when I post to the RCM list - can someone tell
>> me if his analysis is correct?:
>> Thanks,
>> Phil.
>> -------- Original Message --------
>> Subject: Re: FW: Re: [RCU] How to Host Multiple Mail Domains (Email
>> Hosting) in iRedMail Full Featured Linux Mail Server
>> Your mail got altered at the mail server that received kolabsys.com [1]?
>> Authentication-Results: ext-mx-in002.kolabsys.com [2] (amavisd-new);
>>   dkim=pass (1024-bit key) header.d=pricom.com.au [3]
>> 1. When it was received by ext-mx-in002.kolabsys.com [4] from pricom
>> server, your signature was fine and it had passed
>> 2. Something happened on one of these servers ( or
>> which altered the message body, after which your signature no longer
>> verifies.
>> 3. There is no issue with your DKIM-Signature as it verifies on
>> ext-mx-in002.kolabsys.com [4]
>> I have cut-pasted the headers from the original mail below
>> X-Original-To: users at lists.roundcube.net
>> Delivered-To: users-at-lists-dot-roundcube-dot-net at lists.roundcube.net
>> Received: from int-mx001.kolabsys.com [5] (unknown [])
>>   by lists02.kolabsys.com [6] (Postfix) with ESMTP id EDDA7746C1
>>   for <users at lists.roundcube.net>; Tue,  4 May 2021 21:13:56 +0200
>> (CEST)
>> Received: from mx.kolabsys.com [7] (unknown [])
>>   by int-mx001.kolabsys.com [5] (Postfix) with ESMTPS id D9A1713C0376B
>>   for <users at lists.roundcube.net>; Tue,  4 May 2021 21:13:56 +0200
>> (CEST)
>> X-Orig-Spam-Flag: NO
>> X-Orig-Spam-Score: 0.001
>> X-Orig-Spam-Level:
>> X-Orig-Spam-Status: No, score=0.001 tagged_above=-999 required=4.5
>>   tests=[TIME_LIMIT_EXCEEDED=0] autolearn=unavailable
>> Authentication-Results: ext-mx-in002.kolabsys.com [2] (amavisd-new);
>>   dkim=pass (1024-bit key) header.d=pricom.com.au [3]
>> X-Greylist: from auto-whitelisted by SQLgrey-1.8.0
>> DMARC-Filter: OpenDMARC Filter v1.3.2 ext-mx-in002.kolabsys.com [2]
>> 1D8C3EAE
>> Received: from pricom.com.au [3] (pricom.com.au [3] [])
>>   by ext-mx-in002.kolabsys.com [2] (Postfix) with ESMTPS id 1D8C3EAE
>>   for <users at lists.roundcube.net>; Tue,  4 May 2021 21:08:53 +0200
>> (CEST)
>> DKIM-Signature: v=1; a=rsa-sha1; c=relaxed/relaxed;
>>   d=pricom.com.au [3]; s=phr1; x=1620760128; h=MIME-Version:
>> Content-Type:Content-Transfer-Encoding:Date:From:To:Cc:Subject:
>>   Reply-To:In-Reply-To:References:User-Agent:Message-ID; bh=FmYpFg
>>   8n5qzZwGVS9g1ntm5elRA=; b=oRoLjUkhqBD4I7O17UaQEiwoku0KRuVy5/Ghjb
>> 2HhS4HIQMoPOK7JsinkxKUuK4Ux0XJlJAukaD7uSG61aCadR6kRXurcAtSv8kY79
>> w6q2PAf/JPofvR1xVpvN4E1MGqM80s9G6fpvHCdzV0fJKRseoFpZZhkSlctcXPFh
>>   95i5E=
>> MIME-Version: 1.0
>> Links:
>> ------
>> [1] http://kolabsys.com
>> [2] http://ext-mx-in002.kolabsys.com/
>> [3] http://pricom.com.au/
>> [4] http://ext-mx-in002.kolabsys.com
>> [5] http://int-mx001.kolabsys.com/
>> [6] http://lists02.kolabsys.com/
>> [7] http://mx.kolabsys.com/
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