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Re: Last Call: draft-ietf-sieve-refuse-reject (Sieve Email Filtering: Reject and Extended Reject Extensions) to Proposed Standard
Hi Spencer,
My apologies for replying to this message so late, but I was hoping that
the main editor would reply first ;-).
Spencer Dawkins wrote:
I have been selected as the General Area Review Team (Gen-ART)
reviewer for this draft (for background on Gen-ART, please see
http://www.alvestrand.no/ietf/gen/art/gen-art-FAQ.html ).
Please resolve these comments along with any other Last Call comments
you may receive.
Document: draft-ietf-sieve-refuse-reject-07
Reviewer: Spencer Dawkins
Review Date: 2008-08-10
IETF LC End Date: 2008-08-10 (oops!)
IESG Telechat date: N/A
Summary: Almost ready for publication as a Proposed Standard. I have
some clarity questions below, and two technical questions involving
2119 language ...
Comments:
Abstract
This memo updates the definition of the Sieve mail filtering language
"reject" extension, originally defined in RFC 3028.
A "Joe-job" is a spam run forged to appear as though it came from an
Spencer (clarity): I'm OK with the use of "joe-job" (or, at a minimum,
I'm OK with what you guys say it is), but there's not a clear
statement in the abstract that the update to 3028 is in response to
the "joe-job" practice. I'd suggest something like "... originally
defined in RFC 3028, because the definition in RFC 3028 did not allow
messages to be refused during the STMP transaction, and experience has
shown this to be valuable in response to "joe-jobs"."
Sounds good to me.
innocent party, who is then generally flooded by automated bounces,
Message Disposition Notifications (MDNs), and personal messages with
complaints. The original Sieve "reject" action defined in RFC 3028
required use of MDNs for rejecting messages, thus contributing to the
flood of Joe-job spam to victims of Joe-jobs.
This memo updates the definition of the "reject" action to allow
messages to be refused during the SMTP transaction, and defines the
"ereject" action to require messages to be refused during the SMTP
transaction, if possible.
The "ereject" action is intended to replace the "reject" action
wherever possible.
Spencer (clarity): a LOT later in the document, the following text
appears: "The "ereject" action is similar to "reject", but will always
favor protocol level message rejection". That's a really helpful
summary - I'd like to see something like that much earlier in the
document, maybe here.
Ok.
1. Introduction
The Sieve mail filtering language [SIEVEBIS], as originally defined
in RFC 3028 [SIEVE], specified that the "reject" action shall discard
a message and send a Message Disposition Notification [MDN] to the
envelope sender along with an explanatory message. RFC 5228
[SIEVEBIS] does not define any reject action, hence the purpose of
this document.
Spencer (clarity): hmm. I'm almost sure that "The Sieve mail filtering
language [SIEVEBIS]" was NOT "originally defined in RFC 3028
[SIEVE]"... :-) If you drop the first [SIEVEBIS] reference in this
sentence, I think it's correct.
Good point.
Spencer (clarity): It's not particularly easy for me to understand
this paragraph, given that SIEVEBIS is used as the reference for "RFC
5228" in the last sentence. I might suggest "the updated Sieve mail
filtering language [SIEVEBIS] does not define any reject action ..."
Ok.
This document updates the definition of the "reject" action to permit
refusal of the message during the SMTP transaction, if possible, and
defines a new "ereject" action to require refusal of the message
during the SMTP transaction, if possible.
Spencer (clarity): a LOT later in the document, the following text
appears: "The "ereject" action is similar to "reject", but will always
favor protocol level message rejection". That's a really helpful
summary - I'd like to see something like that much earlier in the
document, maybe here.
Ok.
Implementations are further encouraged to use spam-detection systems
to determine the level of risk associated with sending an MDN, and
this document allows implementations to silently drop the MDN if the
rejected message is deemed to be likely spam.
Further discussion highlighting the risks of generating MDNs and the
benefits of protocol-level refusal can be found in [Joe-DoS].
2.1.1. Rejecting a message at the SMTP/LMTP protocol level
Sieve implementations that are able to reject messages at the SMTP/
LMTP level MUST do so and SHOULD use the 550 response code. Note
Spencer (technical): since rejection is a MUST, I'd expect to see
guidance about why using 550 might not be the right thing to do ("why
is this a SHOULD?").
Actually the SHOULD refers to use of other 5XX response codes. Any
suggestions how to make this clearer? Maybe change the first sentence to
read:
Sieve implementations that are able to reject messages at the SMTP/
LMTP level MUST do so using an 4XX or 5XX response code and SHOULD use
the 550 response code.
There's some text at the bottom of 2.5 about using 4XX first, but it
should appear here, I think.
I think you are referring to the following text:
If a Sieve implementation that supports "ereject" does not wish to
immediately disclose the reason for rejection (for example, that it
detected spam), it may delay immediately sending of the 550 error
code by sending a 4XX error code on the first attempt to receive the
message.
While this text can be copied to the section 2.1.1, I think the updated
sentence above is clear enough.
that if a message is arriving over SMTP and has multiple recipients,
some of whom have accepted the message, Section 2.1.2 defines how to
reject such a message.
2.1.2. Rejecting a message by sending a DSN
An implementation may receive a message via SMTP that has more than
one RCPT TO that has been accepted by the server, and at least one
but not all of them are refusing delivery (whether the refusal is
caused by a Sieve "ereject" action or for some other reason). In
this case, the server MUST accept the message and generate DSNs for
all recipients that are refusing it. Note that this exception does
not apply to LMTP, as LMTP is able to reject messages on a per-
recipient basis. (However, the LMTP client may then have no choice
but to generate a DSN to report the error, which may result in
blowback.)
Spencer (clarity): "blowback" isn't defined (yet, at least).
Ok, we will fix.
2.2. Action reject
The "reject" action cancels the implicit keep and refuses delivery of
a message. The reason string is a UTF-8 [UTF-8] string specifying
the reason for refusal. Unlike the "ereject" action described above,
this action would always favor preserving the exact text of the
refusal reason. Typically the "reject" action refuses delivery of a
message by sending back an MDN to the alleged sender (see
Section 2.2.1). However implementations MAY refuse delivery over
protocol (as detailed in Section 2.5), if and only if all of the
Spencer (clarity): "refuse delivery over protocol" reads roughly to
me. is there an adjective for "protocol" that might make this sentence
clearer? i'm not sure that "over protocol" is even required - is it?
It emphasizes that this should happen during delivery, not after it (as
with MDN generation).
if not, you could just delete the two words.
following conditions are true:
Example:
require ["reject"];
if size :over 100K {
reject text:
Your message is to big. If you want to send me a big attachment,
Spencer (nit): s/to/too/ :-)
Thanks.
2.3. Silent upgrade from reject to ereject
Implementations MUST NOT silently upgrade reject actions to ereject
actions, however user interfaces may change the specific action
underlying a descriptive representation, thereby effecting a silent
upgrade of sorts.
Spencer (technical): ??? I may not understand the point here, but from
the user's point of view, the requirement seems religious - protocol
implementations are prohibited from silently upgrading, but user
interfaces aren't, and the effect on the rejected e-mail, from the
user's perspective, is the same, isn't it?
It might or might not be the same from user's perspective.
Some users only care that the message is rejected, other users care that
their rejection reason get sent correctly to the other end.
Or is this talking about "silently upgrading reject actions" without
making sure that the other side is ereject-capable?
I am not sure what do you call "the other side" in this case. Sieve
engine or end user who sent the message being rejected?
Anyway I do agree that this sentence reads awkwardly. It is trying to
say 2 things:
1). Silently upgrading a Sieve script exposed to the user is a bad
thing, because it might change rejection behavior in an expected (to the
script owner) way.
2). But if the reject action is not exposed directly to the user (e.g.
if it is hidden behind some kind of filtering rule UI that never shows
Sieve script to the user, then silently upgrading might be Ok.
Based on this let me try to rephrase this sentence:
Implementations MUST NOT silently upgrade reject actions to ereject
actions in a Sieve script, because this might lead to unpleasant change of
behavior not expected by the owner of the Sieve script.
However user interfaces that hide/don't present generated Sieve scripts
from the user MAY change the specific action, as long as behavior
as far as the user is concerned hasn't changed.
Is this better?