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"." 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. 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. 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 ..." 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. 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?"). There's some text at the bottom of 2.5 about using 4XX first, but it should appear here, I think. 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). 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? 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/ :-) 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? Or is this talking about "silently upgrading reject actions" without making sure that the other side is ereject-capable?