[MlMt] From "XXX via mailmate"

[Bill Cole]

On 2023-12-19 at 07:42:56 UTC-0500 (Tue, 19 Dec 2023 13:42:56 +0100)
MM_Arc via mailmate <mailmate at lists.freron.com>
is rumored to have said:

> Hello,
>
> I notice that some posts on the list have the format “XXX via 
> mailmate” and others don’t.
>
> I’m trying to figure out the reason why

It's because the mailing list software (Mailman 2.x, assuming the 
headers are not being intentionally misleading) is configured to avoid 
having people's posts rejected due to a mail authentication mechanism 
called DMARC. Many-to-many mailing lists such as this one intrinsically 
violate the assumptions of DMARC, which is a tool really designed for 
the needs of big bulk mailers and big mailbox providers.

Mailman modifies the "From" header of messages sent from domains which 
would otherwise be widely rejected (or delivered to a "spam" folder) as 
if they were forged, if they kept the original From header. The DMARC 
protection configuration in Mailman is a complex set of settings that 
varies between lists, and it's a bit of a kludge conceptually, so I 
won't try to pick apart the precise details for this list. Perhaps Benny 
can explain the specific rules.


> and how this can be changed.

To make your messages not have their From "munged" by Mailman, you'd 
need to figure out how to 'game' Mailman to leave them alone. That's 
dependent on your domain's DMARC record in DNS and possibly on the 
configuration of your outbound mail system, e.g. whether and how it 
signs messages using the DKIM mechanism that DMARC utilizes and possibly 
whether you domain has a restricting SPF record.

You cannot change how other people's From headers appear on the messages 
you get from the mailing list. It may be possible to create a custom 
layout for MM to find the hidden 'real' sender address and display that, 
but I'm not sure if Benny has provided enough logic in the layout system 
to support that.

There is probably no solution that you would find satisfying, without 
Benny adding a lot of complex logic to work around the quirks of how 
Mailman can munge headers. I hope he does not make that attempt, as it 
is likely to have a remarkably large number of edge and corner cases.

-- 
Bill Cole
bill at scconsult.com or billcole at apache.org
(AKA @grumpybozo and many *@billmail.scconsult.com addresses)
Not Currently Available For Hire