[Mailman-Users] [Mailman-Developers] Sender field

[John W. Baxter]

On 4/29/06 8:00 AM, "Stephen J. Turnbull" <stephen at xemacs.org> wrote:

> Sender doesn't instruct *conformant* MTAs at all, does it?  AFAIK the
> only thing that a RFC 2821-conforming MTA looks at is the Return-Path
> header, and it's supposed to remove that.

There is no Return-Path: header during transmission of a message. The
Return-Path header is added in the process of delivery.
There is a return path, stated in the MAIL FROM:<example at example.com> SMTP
command.  (That command *can* have more stuff related to authentication.)
The return path is what should be used as the address of a bounce if a mail
system foolishly accepts a message and then creates a bounce.

Notice that if an MTA rejects a message (or one or more of the recipients of
the message), it is not bouncing or creating a bounce.  It is issuing an
error response...the MTA (or MUA in the case of message submission) that was
trying to send creates a bounce message if appropriate (for message
submission, the MUA notifies the user--or pretends to:  Microsoft by default
hides the notification remarkably well).

While multi-line text associated with the rejection code is provided for,
MUAs are very poor about showing it if a submission is rejected--some show
only the first line; some only the last line.  Even some MTAs "improve" the
text of the rejection.

  --John