At 06:40 AM 1/7/2009 -0500, Scott Kitterman wrote:
On Wed, 07 Jan 2009 12:22:24 +0100 Alessandro Vesely
<vesely(_at_)tana(_dot_)it> wrote:
spfdiscuss(_at_)caution(_dot_)icompute(_dot_)com wrote:
The sense I get in other forums is that SPF "can't be used" because it
"breaks forwarding".
One reason why "forwarding" may be considered broken is that that term
doesn't actually have a definite technical meaning in SMTP. To wit,
RFC 5321 added (w.r.t. RFC 2821) an apparently inconsistent phrase
about forwarding. Section 3.9.2 (lists) begins with:
| A mailing list may be said to operate by "redistribution" rather
| than by "forwarding".
apparently implying that "forwarding" is a different operation than
sending mailing list messages. However, the phrase added to the same
paragraph says that:
| the key difference between handling aliases (Section 3.9.1) and
| forwarding (this subsection) is the change to the backward-pointing
| address in this case.
which implies that sending mailing list messages _is_ "forwarding".
The standard literally says that forwarding with a changed return
address is not forwarding. Should that be interpreted like the Baima
Lun saying that a white horse is not a horse?
With a mailing list, a message is sent to the list manager, it is
delivered, and then a new message (with a usually modified body) is created
and sent to the subscriber list. So whatever 'forwarding' is, it's pretty
clearly not a mailing list.
The term "forwarding" can apply to anything from routers, which store and
forward IP datagrams, to any MTA, which stores and forwards an email message.
The best thing to do is agree on terminology at the start of each and every
discussion. It helps to have a webpage, like I do at
http://open-mail.org/MHSmodel.html Then, when the original message in a thread
is forgotten, everyone can refer back to the agreed-on definitions, and avoid a
long discussions where the participants don't even realize they are not talking
about the same thing.
In discussions of email, I prefer to limit the term Forwarding to just Agents
on the Recipient's side of the Border. I use capitalization to show I have
specific definitions in mind. An Agent may operate several MTAs, and
forwarding within that Agent's ADMD (Administrative Management Domain), is not
Forwarding. Forwarding requires a change in the envelope address of the
Recipient, changing at least the domain name in that address.
Using this definition of Forwarding, we can leave out Transmitters and
Remailers. Each of those Agents has an entirely different set of
responsibilities, and calling them forwarders will make a general solution to
the "forwarding problem" extremely difficult, probably impossible. See
http://en.wikipedia.org/wiki/E-mail_forwarding for a discussion of forwarding
vs remailing.
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