dmquigg-spf at yahoo
Jan 7, 2009, 4:53 AM
Post #9 of 53
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> wrote:
>>spfdiscuss [at] caution 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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