Returned mail

[dhog@plan9.cs.su.oz.au dhog@plan9.cs.su.oz.au]

Greg Nenych <gnenych@ncrcan.canada.ATTGIS.COM> wrote:
>Mailers have several things to choose from including "From ", "From: ", and
>"Reply-To: ". Do (or should) any of them use "Sender: "?

No.  Note that "From: " and "Reply-To: " are there for the user agent.  Bounce
messages should never be sent based on these headers.  Rather, they should
use the SMTP "envelope sender" (yes, I'm assuming we're talking SMTP here).
This is frequently stored in the Unix "From " header (YMMV).  Some software
may put it in the "Return-Path: " header.

Mailing list exploders set the envelope sender to the list maintainer, so that
bounces go back to the one person able to do anything about them (eg
unsubscribe them).

Some software throws away the envelope sender and uses the rfc822 From:
header instead.  This is very bad.  It can cause mail loops, resulting in many
many bounce messages in everyone's mail box (this has happened on 9fans).

A lesser sin is for the mail user agent to generate replies based on the envelope
sender.  This is usually easier to fix/work around (just replace the user agent :-).

>> Fans of Plan 9 _want_ to be able
>> to send 8 bit (utf) characters, and most smtp agents will let them (the "cannot"
>> in the message is patently false).
>
>Actually, that's 8/16 bit UTF characters depending on the encoding.

I meant full 8 bit chars as opposed to 7 bit ascii...

Anyway, enough about mail.  Back to Plan 9!