Re: 2821bis chapter 2
John C Klensin <john+smtp@jck.com> Sat, 03 September 2005 15:48 UTC
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Date: Sat, 03 Sep 2005 11:48:55 -0400
From: John C Klensin <john+smtp@jck.com>
To: Frank Ellermann <nobody@xyzzy.claranet.de>, ietf-smtp@imc.org
Subject: Re: 2821bis chapter 2
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--On Saturday, 03 September, 2005 00:46 +0200 Frank Ellermann <nobody@xyzzy.claranet.de> wrote: > > Hi, here's a list of my first observations in 2821bis (-00): > > * 2.3 (terminology) [no new issue] > > I prefer the usual style of 2119 keywords with a reference. The definitions of those terms are different in 2821 than in the 2119 usage, with 2821 following 1123 and related traditions. The difference is significant. Please review the DRUMS archives if you are interested. > * 2.3.1 (deprectation of SOML SAML SEND) [no new issue] > > s/RCPT TO/MAIL FROM/ - the three S??? FROM commands are an > alternative of MAIL FROM in STD 10, not RCPT TO. I wonder how that slipped by. Fixed. > * 2.3.4 (numerical addresses) > > 2821 said "discourged", now it's SHOULD NOT (better). STD 10 > had an obsolete idea of host numbers #<integer> in addition > to domain literals. A leftover from pre-IP days, or at least prior to the distinction between a network part and a local host part of an IP address. IMHO that paragraph needs more clean-up: > > | Hosts are known by names (see the next section); they SHOULD > | NOT be identified by <address-literals> (see section 4.1.2). > | Other forms of numerical addresses are deprecated and MUST > | NOT be used. I've put the forward pointer in. DRUMS pretty much decided to avoid cluttering the 2821 text detailing prohibitions and the #<integer> form is prohibited in A.6.4. So, unless others feel strongly about this, I'm going to leave that last sentence out. > 2.3.8 Originator [no new issue] > > ? An "originating" system (sometimes called an SMTP > originator) ? introduces mail into the Internet or, more > generally, into a ? transport service environment. > > That's a very tricky statement. Internet mail is not limited > to SMTP, and SMTP is (in theory) not limited to the Internet. > How about this: > > | An "originating" system (sometimes called an SMTP originator) > | introduces mail into the transport service environment > defined | by this document, i.e. SMTP in the Internet. The tricky wording was intentional, given the gateway/relay family of issues. It may well be too subtle, but the suggested replacement text, IMO, narrows things too much. Comments and suggestions from others solicited. > At the end of 2.3.8: > > [[Note in draft/Placeholder: There has been a request to > expand this > > Yes, something about gateways acting as SMTP originator. They > should not invent a Return-Path to the mail-originator, unless > they are also the MX and / or it's clearly in the best interest > of the mail originator. This is tricky, and, again, more discussion is requested. I would suggest that, if the gateway cannot determine a reverse path (not the header Return-Path, which can be supplied only by the delivery MTA), then either (i) it has no business injecting the mail into the SMTP environment or (ii) it is acting, not as a gateway, but as a submission server. The fact that the mail originated on another system, in a different format or protocol, is almost irrelevant to a submission server, it presumably has, and follows, its own sender-authorized rules about how to set the reverse path. Or perhaps I don't understand what you are suggesting at all, since there is no way to initiate a mail transaction without a MAIL command, and there is no valid syntax for a MAIL command that doesn't contain a reverse-path. > * 2.3.9 typo: s/2979 [18]/2045 [19]/ but keep 2979 in 2.3.8 Gack. Fixed. > * 2.4 (minor nits) [no new issue] > > ? In some commands and replies, arguments MUST follow the verb > | In some commands and replies, arguments follow the verb Rephrased. > ? This is NOT true of a mailbox local-part. > | This is generally not true of a mailbox local-part. > > The 1024 exceptions are specified elsewhere in the text. Or > kill this sentence, the same idea is repeated often enough in > the text. Sentence killed. > ? A few SMTP servers, in violation of this specification (and > RFC 821) ? require that command verbs be encoded by clients in > upper case. ? Implementations MAY wish to employ this encoding > to accommodate those ? servers. > > Please remove this, non-conforming servers are out of scope. Opinions from others solicited, but this is an important interoperability constraint in the real world and, if I recall, DRUMS discussed the issue at some lengths. > ? receiving SMTP servers MAY clear the high-order bit or reject > | receiving SMTP servers SHOULD reject > > Good enough to please stupid MUAs. 2821 was way too "liberal". > We're probably not interested in strange effects for 0x80 etc. > ? Delivery SMTP systems MAY reject ("bounce") such messages > | Delivery SMTP systems MAY reject such messages > > Please let's reserve "bounce" for "bounce messages" (NDNs), > i.e. the client. If an MDA creates a bounce after the MX > accepted the crap, then it's almost certainly net abuse. I'm not quite sure what you are getting at here, partially because, in the 2821 model, there is no such entity as an MDA. Note that "bounce" is used again in 3.4 (first bullet after "Alternately"). And remember that the "subsequent failure" text in 3.3 and much of section 6 is tied up with the explicit permission for an receiving MTA to accept all of the RCPT commands and delivery addresses, accept the message body itself (DATA...354...CRLF.CRLF... 250) and then bounce (sic) the message by sending back mail with a null reverse path. > ? Eight-bit message content transmission MAY be requested > [...] > ? encoding; servers MAY reject such messages. > > For obscure reasons the very same concept is often repeated > several times (and in the same section). Please delete this > paragraph, making the text longer by repetitions doesn't help. The "obscure reasons" are too much slicing, dicing, and pasting. Your general observation is certainly true, and I'd appreciate more pointers to redundant text that can be replaced by cross-references or removed entirely. But I'm not sure I see the redundancy here: Paragraph 6 of Section 2.4 ("Commands and replies are composed...") say that unextended mail transactions must not send 8bit information at all. It could use a forward reference to paragraph 7, which I have inserted. Given other work now going on (see, e.g., draft-klensin-emailaddr-i18n-03, the expired draft-hoffman-utf8headers-00, or draft-lee-jet-ima-00), it might even be wise to modify the initial sentence in that paragraph to make the "unless extended" distinction clear there too. Paragraph 7 ("Eight-bit message content transmission...") then talks about the specific 8BITMIME extension. If one were a purist, one could argue for removing that because it really is and extension and not an base SMTP problem. But its use is recommended, it is widely supported today, and it does imply changes to the transport environment, so leaving it in seems appropriate. > ? The metalinguistic notation used in this document corresponds > [...] > ? are surrounded by pointed brackets (e.g., <CRLF>) for > clarity. > > That paragraph should be section 1.3, not the end of chapter 2 > near page 17, With pointers to 2234bis and 2119 in chapter 1 > all explanations of CRLF, CR, LF, MUST, MAY, etc. in chapter 2 > could be eliminated. I agree that it would be better to move that text. Let me see what I can do with it. See above for the 2119 issue. > What I really wanted was to create some kind of "collected > ABNF" for 2821bis, so I better stop my nit-picking here at the > end of chapter 2 (jumping to the ABNF in chapter 4 in another > article). Ok. But note that, given the ABNF errors that have been found in 2821 (and in 2822) after careful checking by multiple people, you should expect to encounter some resistance to any sweeping changes or sets of equivalent productions. If they clarify things enough they may be worth making, but the clarification advantages have to be balanced against the risk of making new sets of errors. > Generally: The default SMTP use today is "spam", abuse, and > spam-related messages (bogus bounces etc.). Therefore the > default action in any case of doubt MUST be "reject a.s.a.p.". Frank, I don't know how, or if, either of us is going to persuade the other, but I'm operating under three assumptions with this draft and will continue to do so unless the ADs or some appropriately-chartered WG tells me otherwise. Those assumptions are: (i) The goal of this revision effort is to clean up errors and bad text to the extent necessary to move 2821bis forward to Draft Standard. This is not a "revise SMTP" or "change mail philosophy" effort. (ii) The ground rules for this effort are the same as those for DRUMS, i.e., clarification and consolidations of the base specifications and documentation of contemporary practice consistent with those specifications, not insertion of new features or ways of doing things. Those two assumptions are obviously closely related to each other. The third very nearly follows from the other two, but is a statement about philosophy: (iii) Whether via extensions or other add-ons, changes in operational practices, or changes in laws and consequent enforcement, we will get the spam and abuse situations under control. When we do, we will still want a mail system that is optimized for the efficient and reliable delivery of email. Such a system tries to deliver messages and reliably report what cannot be delivered. It is designed around very high expectations that a legitimate user, even an anonymous one, sending interpersonal mail to a legitimate user or mailbox, will see that mail delivered, and delivered quickly. It does not look for excuses to discard messages because they do not conform to one rule or another. Changing the base SMTP specification in significant ways to accommodate the short-term battle against spam or other forms of abuse in ways that violate those assumptions is pathological because, on one hand, it gives us a damaged mail structure forever. Conversely, if the hypothesis that we will get the present situation under control is false, SMTP modifications are not going to be sufficient: we will need a permission-based, or rigid-authority-based, mail system and SMTP will die regardless of what tuning-level changes are made to it. regards, john
- 2821bis chapter 2 Frank Ellermann
- Re: 2821bis chapter 2 Tony Finch
- Re: 2821bis vs rfc2119 Frank Ellermann
- Re: 2821bis vs rfc2119 wayne
- Re: 2821bis chapter 2 John C Klensin
- Re: 2821bis chapter 2 Frank Ellermann
- Re: 2821bis chapter 2 John Leslie
- Re: 2821bis chapter 2 John Leslie
- Re: 2821bis chapter 2 John C Klensin
- RFC2821bis-01 Issue 7: Use of 2119 definitions fo… John C Klensin
- Re: 2821bis chapter 2 Frank Ellermann
- Re: 2821bis chapter 2 Frank Ellermann
- Re: RFC2821bis-01 Issue 7: Use of 2119 definition… Frank Ellermann
- Re: RFC2821bis-01 Issue 7: Use of 2119 definition… Tony Hansen