On Thu, 27 Nov 2008, Oliver Stöneberg wrote:
> Quoting RFC 2821 section 6.1:
>
> If there is a delivery failure after acceptance of a message, the
> receiver-SMTP MUST formulate and mail a notification message.
> This
> notification MUST be sent using a null ("<>") reverse path in the
> envelope. The recipient of this notification MUST be the address
> from the envelope return path (or the Return-Path: line).
> However,
> if this address is null ("<>"), the receiver-SMTP MUST NOT send a
> notification. Obviously, nothing in this section can or should
> prohibit local decisions (i.e., as part of the same system
> environment as the receiver-SMTP) to log or otherwise transmit
> information about null address events locally if that is desired.
> If
> the address is an explicit source route, it MUST be stripped down
> to
> its final hop.
>
> XMail doesn't set the "Return-Path" header at all, so the non-
> delivery reports are not following the RFC.
The Return-Path header must be set only when SMTP servers do the "final
delivery" on the recipient mailbox.
An MTA->MTA message must not set Return-Path. XMail inserts the
Return-Path only when dropping messages inside its own mailboxes (final
deliveries).
"When the delivery SMTP server makes the "final delivery" of a
message, it inserts a return-path line at the beginning of the mail
data. This use of return-path is required; mail systems MUST support
it. The return-path line preserves the information in the <reverse-
path> from the MAIL command. Here, final delivery means the message
has left the SMTP environment. Normally, this would mean it had been
delivered to the destination user or an associated mail drop, but in
some cases it may be further processed and transmitted by another
mail system."
Note that there are historical issues about the Return-Path, and note the
phrase "message has left the SMTP environment". In todays infrastrucutre,
the SMTP "environment" is left only when a message is finally delivered.
- Davide
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