[Mailman-Users] From field displayed by MS Outlook

Barry Warsaw barry at python.org
Thu Jan 22 22:26:18 CET 2004

On Thu, 2004-01-22 at 15:39, Richard Barrett wrote:

> And I did not say it would. Nor is it necessary to so do. Outlook is 
> not wrong and nor is Mailman. Its just that some users are confused by 
> what they see and some mailing list admins are equally confused about 
> why their users are confused.

That's good, because I'm confused about why those users are confused
too!  Is it just that they're seeing stuff in the From field that
they're not used to seeing?

But let's examine the use of the Sender field in the first place.  RFC
2822 says that "sender MUST occur with multi-address from".  Well,
generally the From header just contains the address of the poster.  Even
when we anonymize it, there will normally be just one address in the
>From header.

RFC 2822 goes on to explain the intended use of the originator fields in
section 3.2.6.  Quoting:

        The "Sender:" field specifies the mailbox of the agent
        responsible for the actual transmission of the message.  For
        example, if a secretary were to send a message for another
        person, the mailbox of the secretary would appear in the
        "Sender:" field and the mailbox of the actual author would
        appear in the "From:" field.

Who's the agent responsible for the actual transmission of the message? 
Is Mailman acting as this agent?  Arguably not.  If we interpret things
this way, then Mailman shouldn't be adding any Sender header.  Bounces
/should/ still go to the right place because that will always be
specified as the envelope sender, i.e. the SMTP MAIL FROM: address. 
Some remote MTAs may do the wrong thing when it sees messages for which
we haven't munged Sender, but then that wouldn't be Mailman's problem
would it? <wink>

Perhaps the right fix for Mailman is to not touch the Sender header at
all.  If one is there, leave it.  If not, don't add one.  This makes me
nervous though because maybe the voodoo about Sender and bounce backs is

One other thing.  Mailman also adds an Errors-To header with the same
envelope sender address.  Errors-To isn't described in RFC 2822, and
it's described as non-standard, discouraged in RFC 2076.  This latter
recommends Return-Path instead, so even there maybe Mailman isn't doing
quite the right thing.  (It's not clear to me whether Outlook is
conflating From and Return-Path also, though.)

If you want to play with this, then patch
Mailman/Handlers/SMTPDirect.py.  Look down at the bulkdeliver()
function.  You could try commenting out the "del msg['sender']" line and
"msg['Sender'] = envsender" line.  Also try changing the Errors-To
fields to Return-Path.  See comments I just added to the file in CVS.

If you do try this, please report back here with your results.  Are the
various Outlooken behaving in a less confusing way?  Are your bounces
still going to the right place?  For VERPs and non-VERPs?  (This might
be hard to tell, due to the plethora of mail servers out there.)


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