[Mailman-Users] cause of bounces

[Mark Sapiro]

On 10/17/2017 04:46 PM, Grant Taylor via Mailman-Users wrote:
> 
> I decided to see if there was an update to RFC 5322, and lo and behold
> there is.  RFC 6854, which specifically updates RFC 5322 section 3.6.2
> and allows group address syntax exists.
> 
> TL;DR:  From: can now contain a Group address / name, which can zero or
> one or more mailbox addresses.
> 
> I feel like RFC 6854 provides some light at the end of the tunnel and
> allows mailing list managers to modify the From: to be the group,
> including the Group's address.


Group address syntax is something else. it is a specific syntax which is
a name followed literally by a colon followed by a list of zero or more
mailboxes (email addresses) and terminated by a semicolon.

E.g., from the RFC

   Second, consider an email message that is meant to be "from" the two
   managing partners of a business, Ben and Carol, and that is sent by
   their assistant, Dave.  This message could always have been presented
   this way:

      From: ben at example.com,carol at example.com
      Sender: dave at example.com

   This change allows it to be represented this way:

      From: Managing Partners:ben at example.com,carol at example.com;
      Sender: dave at example.com

The group syntax has always been allowed in To: and some other headers.
RFC 6854 just extends it to From:

This is most commonly seen with some MUAs when all the recipients are
Bccs, the message is

To: undisclosed recipients:;

> Sender: is not needed because it would be the same as the Group's from
> address.


There's no such thing as a group's address unless the addresses are
listed along with the group name.

Anyway, using a group name alone as From: avoids DMARC as there is no
From: address domain for a DMARC lookup.


> Similarly, I found wording in RFC 5322 that indicates that a user agent
> forwarding a message, is actually a new message.  Section 3.6.6 has the
> following copy:
> 
>>     Note: Reintroducing a message into the transport system and using
>> resent fields is a different operation from "forwarding".
>>  "Forwarding" has two meanings: One sense of forwarding is that a mail
>> reading program can be told by a user to forward a copy of a message
>> to another person, making the forwarded message the body of the new
>> message.  A forwarded message in this sense does not appear to have
>> come from the original sender, but is an entirely new message from the
>> forwarder of the message.  Forwarding may also mean that a mail
>> transport program gets a message and forwards it on to a different
>> destination for final delivery.  Resent header fields are not intended
>> for use with either type of forwarding.


That type of forwarding is exactly what is done by Mailman's DMARC Wrap
Message action and that is the reason that action exists. Because in
that case the list message is RFC 5322 compliant. However many MUAs,
particularly mobile apps, have difficulty rendering such a message in a
good way, so Wrap Message isn't always the best option.

-- 
Mark Sapiro <mark at msapiro.net>        The highway is for gamblers,
San Francisco Bay Area, California    better use your sense - B. Dylan