Can I fix this groups.io problem with a send hook or something

[Ian Zimmerman]

On 2020-11-24 17:22, Chris Green wrote:

> > > I'm on a couple of mailing lists that have recently moved from
> > > Yahoo Groups to groups.io.  For DMARC (so they claim) groups.io
> > > change the senders E-mail address as follows:-
> > > 
> > >     Sender Name <sender.name at btinternet.com>
> > > 
> > > becomes:-
> > > 
> > >     "Sender Name via groups.io" <sender.name=btinternet.com at groups.io>

> It only happens to users from some domains.  I have seen it only with
> btinternet.com and ntlworld.com.  Like you I can send replies off-list
> to senders from other domains such as gmail and my own isbd.net.
> 
> There is a faq entry about it on the groups.io web site, that's where
> I found it has something to do with DMARC.

It is because those senders subscribed with an address covered by a
strict DMARC policy. If their address is not munged by the list, their
messages will be bounced back to the list by almost everyone if they
fail a DKIM check (and that's almost always).

This is just a perfect storm of sh*t - DMARC misguided by itself (IMO)
plus the ancient but misguided (also IMO) practice of lists munging or
adding to message contents.

There's no good automatic solution to build into a MUA for this, as far
as I know. The best you can do is write a macro to extract the true
sender, and feel lucky for using a MUA that allows that :-)

-- 
Ian