[ On Saturday, June 25, 2005 at 15:04:27 (+0200), Jakob Hirsch wrote: ]
> Subject: Re: [exim] a large number of domains fronted by Exim are refusing
> bounces...
>
> Empty return path means the message is generated by some machine, not a
> human, right?
Not necessarily -- you seem to be confusing the concepts here.
> So if the recipient address is never used for outgoing
> mail, why in the world should any machine send mail to this address?
You seem to think that anything, agent or human, sending mail has to
have a mailbox address. That's simply not true.
Often there is no "recipient" user/mailbox in the first place for agents
which send messages with a null reverse path. That's part of what the
null reverse path is for to start with -- i.e. to be able to send mail
without having a valid, non-null, return address!
Please pay close attention to all the hints in this section from the
SMTP protocol standard:
4.5.5 Messages with a null reverse-path
There are several types of notification messages which are required
by existing and proposed standards to be sent with a null reverse
path, namely non-delivery notifications as discussed in section 3.7,
other kinds of Delivery Status Notifications (DSNs) [24], and also
Message Disposition Notifications (MDNs) [10]. All of these kinds of
messages are notifications about a previous message, and they are
sent to the reverse-path of the previous mail message. (If the
delivery of such a notification message fails, that usually indicates
a problem with the mail system of the host to which the notification
message is addressed. For this reason, at some hosts the MTA is set
up to forward such failed notification messages to someone who is
able to fix problems with the mail system, e.g., via the postmaster
alias.)
All other types of messages (i.e., any message which is not required
by a standards-track RFC to have a null reverse-path) SHOULD be sent
with with a valid, non-null reverse-path.
Implementors of automated email processors should be careful to make
sure that the various kinds of messages with null reverse-path are
handled correctly, in particular such systems SHOULD NOT reply to
messages with null reverse-path.
Note that automated e-mail processors are not required to use a non-null
reverse path -- though they are strongly encouraged to do so. Indeed
agents acting on the behalf of users, e.g. handling incoming messages to
users and sending automated replies to those messages, such as vacation
notices, should send those reply using a sender address that will be
returned to the same user.
--
Greg A. Woods
H:+1 416 218-0098 W:+1 416 489-5852 x122 VE3TCP RoboHack <[EMAIL PROTECTED]>
Planix, Inc. <[EMAIL PROTECTED]> Secrets of the Weird <[EMAIL
PROTECTED]>
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