[Mailman-Users] Re: Addressing of list messages by the server

[Mark Sapiro]

On 2/10/21 9:26 AM, Christian Buser via Mailman-Users wrote:
> 
> I have been asked by one of our list members about why the addressing of list 
> messages he receives varies and he likes to know why. 
> 
> Some messages come with the following headers: 
> 
> From: Sender Name via Listname 
> To: listn...@domain.com
> Cc: Recepient Name 


This is a message which has had the DMARC mitigation `Munge From` applied.

If the Cc: is actually a recipient, it was put there by the sender, but
I suspect it is actually the sender's address and not the recipient's.
In the case of Munge From, the sender's address is put either in Cc: or
Reply-To: depending on other list settings. See

for more detail on this.


> Other messages (on the same list, same recipient): 
> 
> From: Sender Name  <>
> To: Listname 
> (and no Cc: header)


This is a message to which DMARC mitigation has not been applied.


> My questions - just to understand it, since the list seems to work perfectly:
> 
> 1) What does cause this different addressing

The list is applying DMARC Munge From mitigations based on the DMARC
policy of the original From: domain. See
 for more about this.


> 2) How does the receiving mail server know where to deliver the message when 
> there is no Cc: field in the headers and the list address in the To: field? 


The recipients of the message are specified as recipients by Mailman in
its SMTP transaction with the outgoing MTA. These are known as envelope
recipients and are the addresses to which the message will be sent. They
have nothing to do with any To: or Cc: headers in the message itself.

-- 
Mark Sapiro The highway is for gamblers,
San Francisco Bay Area, Californiabetter use your sense - B. Dylan
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[Mailman-Users] Re: Addressing of list messages by the server

[Grant Taylor via Mailman-Users]

On 2/10/21 10:26 AM, Christian Buser via Mailman-Users wrote:

Hi all


Hi,

My questions - just to understand it, since the list seems to work 
perfectly:


1) What does cause this different addressing


I'm guessing this is related to DMARC.

2) How does the receiving mail server know where to deliver the message 
when there is no Cc: field in the headers and the list address in 
the To: field?


Email is delivered based on the SMTP envelope addresses, which are 
completely disconnected (but often similar) to the email header addresses.



Thank you, Christian


You're welcome.



--
Grant. . . .
unix || die



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