[mlmmj] DMARC

[mlmmj] DMARC

[Richard Torrens (lists)]

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My server uses Exim and mlmmj. I did not set it up - it's a virtual linux
account so I have no sudo access.

One of the mailing lists I run has a problem with DMARC - from one user!
Every time this use posts there are a load of one-off bounces because that
DMARC verification has failed.

The member concerned is @casema.nl 

Other members postings nerver bounce for that reason. It's clear that
casema.nl must have a stringent policy, but I cannot find out what is
causing the problem.

Has anyone any hints or suggestions?

mlmmj-sub version 1.2.15

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-- 
Richard Torrens.
http://www.Torrens.org for genealogy, natural history, wild food, walks, cats
and more!

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Re: [mlmmj] DMARC

[Geert Stappers]

On Mon, Mar 02, 2020 at 11:13:51AM +0000, Richard Torrens (lists) wrote:
> My server uses Exim and mlmmj. I did not set it up - it's a virtual linux
> account so I have no sudo access.
> 
> One of the mailing lists I run has a problem with DMARC - from one user!
> Every time this use posts there are a load of one-off bounces because that
> DMARC verification has failed.
> 
> The member concerned is @casema.nl 
> 
> Other members postings nerver bounce for that reason. It's clear that
> casema.nl must have a stringent policy, but I cannot find out what is
> causing the problem.
> 
> Has anyone any hints or suggestions?

Consider the mailinglist a "man in the middle"



> 
> mlmmj-sub version 1.2.15
> 
> Attached:
>   customheaders
>   delheaders
> 
 

> Reply-To: StrongED@Torrens.org
> List-Id: RISC OS StrongED mailing list
> Sender: StrongED Mailing List <StrongED@Torrens.org>
> List-Unsubscribe: <StrongED+unsubscribe@Torrens.org>

> X-ThisMailContainsUnwantedMimeParts:
> Return-Receipt-To:



Regards
Geert Stappers
-- 
Silence is hard to parse

Re: [mlmmj] DMARC

[Christof Thalhofer]

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Am 02.03.20 um 12:13 schrieb Richard Torrens (lists):

> The member concerned is @casema.nl 
> 
> Other members postings nerver bounce for that reason. It's clear that
> casema.nl must have a stringent policy, but I cannot find out what is
> causing the problem.
> 
> Has anyone any hints or suggestions?

Please have a look at the nameserver TXT reponse for _dmarc.casema.nl:

> dig -t TXT  _dmarc.casema.nl 
> 
> ; <<>> DiG 9.11.3-1ubuntu1.11-Ubuntu <<>> -t TXT _dmarc.casema.nl
> ;; global options: +cmd
> ;; Got answer:
> ;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 47619
> ;; flags: qr rd ra; QUERY: 1, ANSWER: 1, AUTHORITY: 0, ADDITIONAL: 1
> 
> ;; OPT PSEUDOSECTION:
> ; EDNS: version: 0, flags:; udp: 512
> ;; QUESTION SECTION:
> ;_dmarc.casema.nl.		IN	TXT
> 
> ;; ANSWER SECTION:
> _dmarc.casema.nl.	3600	IN	TXT	"v=DMARC1; p=reject; rua=mailto:jn2qdxcl@ag.dmarcian.eu; ruf=mailto:jn2qdxcl@fr.dmarcian.eu; fo=1; adkim=s; aspf=s;"

They say, reject every mail that is supposed to come from casema.nl but
was sent from a server not being part of this domain.

The user xyz@casema.nl sent a mail to the mailinglist, the ML server
sends the mail to various recipients. The ML server is not part of
casema.nl.

The receiving mailservers ask the nameservers of casema.nl who is
allowed to send mails in the name of casema.nl. Because the mailserver
of the mailinglist is not, they reject the mail.


Alles Gute

Christof Thalhofer

-- 
Dies ist keine Signatur


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