LEMONADE D. Cridland, Ed. Internet-Draft A. Melnikov, Ed. Intended status: Standards Track Isode Limited Expires: October 5, 2007 S. Maes, Ed. Oracle April 3, 2007 The Lemonade Profile draft-ietf-lemonade-profile-bis-05.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on October 5, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document describes a profile (a set of required extensions, restrictions and usage modes) of the IMAP and mail submission protocols. This profile allows clients (especially those that are constrained in memory, bandwidth, processing power, or other areas) to efficiently use IMAP and Submission to access and submit mail. This includes the ability to forward received mail without needing to Cridland, et al. Expires October 5, 2007 [Page 1] Internet-Draft Lemonade Profile April 2007 download and upload the mail, to optimize submission and to efficiently resynchronize in case of loss of connectivity with the server. The Lemonade profile relies upon several extensions to IMAP and Mail Submission protocols. Table of Contents 1. Conventions used in this document . . . . . . . . . . . . . . 4 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Summary of the required support . . . . . . . . . . . . . . . 5 3.1. Lemonade Submission Servers . . . . . . . . . . . . . . . 5 3.2. Lemonade Message Stores . . . . . . . . . . . . . . . . . 6 4. Lemonade Submission Servers . . . . . . . . . . . . . . . . . 7 4.1. Forward Without Download . . . . . . . . . . . . . . . . . 7 4.2. Pipelining . . . . . . . . . . . . . . . . . . . . . . . . 7 4.3. DSN Support . . . . . . . . . . . . . . . . . . . . . . . 7 4.4. Message size declaration . . . . . . . . . . . . . . . . . 7 4.5. Enhanced status code Support . . . . . . . . . . . . . . . 8 4.6. Encryption and Compression . . . . . . . . . . . . . . . . 8 5. Lemonade Message Stores . . . . . . . . . . . . . . . . . . . 9 5.1. Quick resynchronization . . . . . . . . . . . . . . . . . 9 5.2. Message part handling . . . . . . . . . . . . . . . . . . 9 5.3. Compression . . . . . . . . . . . . . . . . . . . . . . . 10 5.4. In band notifications . . . . . . . . . . . . . . . . . . 10 5.5. Searching and View Filters . . . . . . . . . . . . . . . . 10 5.6. Mailbox Handling . . . . . . . . . . . . . . . . . . . . . 11 5.7. Forward Without Download . . . . . . . . . . . . . . . . . 11 5.8. Additional IMAP extensions . . . . . . . . . . . . . . . . 11 5.9. Registration of $Forwarded IMAP keyword . . . . . . . . . 11 6. Lemonade Mail User Agents . . . . . . . . . . . . . . . . . . 12 7. Forward without download . . . . . . . . . . . . . . . . . . . 12 7.1. Motivations . . . . . . . . . . . . . . . . . . . . . . . 12 7.2. Message Sending Overview . . . . . . . . . . . . . . . . . 13 7.3. Traditional Strategy . . . . . . . . . . . . . . . . . . . 13 7.4. Step by step description . . . . . . . . . . . . . . . . . 14 7.4.1. Message assembly using IMAP CATENATE extension . . . . 15 7.4.2. Message assembly using SMTP CHUNKING and BURL extensions . . . . . . . . . . . . . . . . . . . . . . 19 7.5. Security Considerations for pawn-tickets. . . . . . . . . 23 7.6. Copies of Sent messages: The fcc problem . . . . . . . . . 23 8. OMA MEM Requirement document . . . . . . . . . . . . . . . . . 24 8.1. OMA MEM Architecture . . . . . . . . . . . . . . . . . . . 24 8.2. OMA MEM Deployment Issues . . . . . . . . . . . . . . . . 24 8.3. OMA MEM proxy . . . . . . . . . . . . . . . . . . . . . . 24 8.4. IETF Lemonade Architecture . . . . . . . . . . . . . . . . 25 Cridland, et al. Expires October 5, 2007 [Page 2] Internet-Draft Lemonade Profile April 2007 8.5. Lemonade profile logical architecture . . . . . . . . . . 26 8.5.1. Relationship between the OMA MEM and Lemonade logical architectures . . . . . . . . . . . . . . . . 26 8.5.2. Lemonade realization of OMA MEM with non-Lemonade compliant servers . . . . . . . . . . . . . . . . . . 28 8.6. Filters and server to client notifications and Lemonade . 29 9. Deployment Considerations . . . . . . . . . . . . . . . . . . 31 10. Security Considerations . . . . . . . . . . . . . . . . . . . 31 10.1. Confidentiality Protection of Submitted Messages . . . . . 31 10.2. TLS . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 10.3. Additional extensions and deployment models . . . . . . . 32 11. IANA considerations . . . . . . . . . . . . . . . . . . . . . 32 12. Version history . . . . . . . . . . . . . . . . . . . . . . . 32 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 33 14. References . . . . . . . . . . . . . . . . . . . . . . . . . . 34 14.1. Normative References . . . . . . . . . . . . . . . . . . . 34 14.2. Informative References . . . . . . . . . . . . . . . . . . 36 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 37 Intellectual Property and Copyright Statements . . . . . . . . . . 39 Cridland, et al. Expires October 5, 2007 [Page 3] Internet-Draft Lemonade Profile April 2007 1. Conventions used in this document In examples, "M:", "I:" and "S:" indicate lines sent by the client messaging user agent, IMAP e-mail server and SMTP submit server respectively. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [KEYWORDS]. Other capitalised words are typically names of extensions or commands - these are uppercased for clarity only, and are case-insensitive. All examples in this document are optimized for Lemonade use and might not represent examples of proper protocol usage for a general use Submit/IMAP client. In particular examples assume that Submit and IMAP servers support all Lemonade extensions described in this document, so they do not demonstrate fallbacks in the absence of an extension. 2. Introduction The Lemonade Profile, or simply Lemonade, provides enhancements to Internet email to support diverse service environments. Lemonade Mail Servers provide both a Lemonade Submission Server and a Lemonade Message Store, which are based on the existing [SUBMIT] and [IMAP] protocols respectively. This document describes the Lemonade profile that includes: o General common enhancements to Internet Mail, described in Section 5 and Section 4. o "Forward without download" that describes exchanges between Lemonade clients and servers to allow to submit new email messages incorporating content which resides on locations external to the client, described in Section 7. o Quick mailbox resynchronization, described in Section 5.1. o Extensions to support more precise, and broader, notifications from the store in support of notifications and view filters, described in Section 5.4 and Section 5.5. It is intended that the Lemonade profile support realizations of the OMA's mobile email enabler (MEM) (see [MEM-req] and [MEM-arch]) using Internet Mail protocols defined by the IETF. Cridland, et al. Expires October 5, 2007 [Page 4] Internet-Draft Lemonade Profile April 2007 3. Summary of the required support 3.1. Lemonade Submission Servers Lemonade Submission Servers MUST provide a service as described in [SUBMIT], and MUST support the following. Note that the Lemonade Profile imposes further requirements for some cases, detailed in the sections cited. +---------------------+--------------------+--------------+ | SMTP extension | Reference | Requirements | +---------------------+--------------------+--------------+ | PIPELINING | [SMTP-PIPELINING] | Section 4.2 | | DSN | [SMTP-DSN] | Section 4.3 | | SIZE | [SMTP-SIZE] | Section 4.4 | | ENHANCEDSTATUSCODES | [SMTP-STATUSCODES] | Section 4.5 | | STARTTLS | [SMTP-TLS] | Section 4.6 | | BURL imap | [SMTP-BURL] | Section 7 | | BINARYMIME | [SMTP-BINARYMIME] | Section 4.1 | | CHUNKING | [SMTP-BINARYMIME] | Section 4.1 | | 8BITMIME | [SMTP-8BITMIME] | [SMTP-BURL] | | AUTH | [SMTP-AUTH] | [SUBMIT] | | QUICKSTART | | Section 4.6 | +---------------------+--------------------+--------------+ Cridland, et al. Expires October 5, 2007 [Page 5] Internet-Draft Lemonade Profile April 2007 3.2. Lemonade Message Stores Lemonade Message Stores MUST provide a service as described in [IMAP], and MUST support the following. Note that the Lemonade Profile imposes further requirements for some cases, detailed in the sections cited. +------------------+------------------+--------------+ | IMAP extension | Reference | Requirements | +------------------+------------------+--------------+ | NAMESPACE | [IMAP-NAMESPACE] | Section 5.6 | | CONDSTORE | [IMAP-CONDSTORE] | Section 5.1 | | STARTTLS | [IMAP] | - | | URLAUTH | [IMAP-URLAUTH] | Section 5.7 | | CATENATE | [IMAP-CATENATE] | Section 5.7 | | UIDPLUS | [IMAP-UIDPLUS] | Section 5.7 | | LITERAL+ | [IMAP-LITERAL+] | Section 5.8 | | IDLE | [IMAP-IDLE] | Section 5.4 | | NOTIFY | [IMAP-NOTIFY] | Section 5.4 | | $Forwarded | - | Section 5.9 | | BINARY | [IMAP-BINARY] | Section 5.2 | | QRESYNC | [IMAP-QRESYNC] | Section 5.1 | | ESEARCH | [IMAP-ESEARCH] | Section 5.5 | | WITHIN | [IMAP-WITHIN] | Section 5.5 | | CONTEXT | [IMAP-CONTEXT] | Section 5.5 | | CONVERT | [IMAP-CONVERT] | Section 5.2 | | COMPRESS=DEFLATE | [IMAP-COMPRESS] | Section 5.3 | | METADATA | [IMAP-METADATA] | Section 5.8 | | LIST-EXTENDED | [IMAP-LISTEXT] | Section 5.8 | +------------------+------------------+--------------+ Cridland, et al. Expires October 5, 2007 [Page 6] Internet-Draft Lemonade Profile April 2007 4. Lemonade Submission Servers All Lemonade Submission Servers implement the Mail Submission protocol described in [SUBMIT], which is in turn a specific profile of [ESMTP]. Therefore any MUA designed to submit email via [SUBMIT] or [ESMTP] will interoperate with Lemonade Submission Servers. In addition, Lemonade Submission Servers implement the following set of SMTP and Submission extensions to increase message submission efficiency. 4.1. Forward Without Download In order to optimize network usage for the typical case where message content is copied to, or sourced from, the IMAP store, Lemonade provides support for a suite of extensions collectively known as Forward Without Download, discussed in detail in Section 7. Lemonade Submission Servers MUST support the BURL [SMTP-BURL], 8BITMIME [SMTP-8BITMIME], BINARYMIME [SMTP-BINARYMIME] and CHUNKING [SMTP-BINARYMIME]. BURL MUST support URLAUTH type URLs [IMAP-URLAUTH], and thus MUST advertise the "imap" option following the BURL EHLO keyword (See [SMTP-BURL] for more details). 4.2. Pipelining Some clients regularly use networks with a relatively high latency, such as Mobile or Satellite based networks. Avoidance of round-trips within a transaction has a great advantage for the reduction in both bandwidth and total transaction time. For this reason Lemonade compliant mail submission servers MUST support the SMTP Service Extensions for Command Pipelining [SMTP-PIPELINING]. In addition, Lemonade Submission Servers provide full support for the QUICKSTART framework described in . 4.3. DSN Support Lemonade compliant mail submission servers MUST support SMTP service extensions for delivery status notifications [SMTP-DSN]. 4.4. Message size declaration There is a distinct advantage in detecting failure cases as early as possible in many cases, such as where the user is charged per-octet, or where bandwidth is low. This is especially true of large message Cridland, et al. Expires October 5, 2007 [Page 7] Internet-Draft Lemonade Profile April 2007 sizes. Lemonade Submission Servers MUST support the SMTP Service Extension for Message Size Declaration [SMTP-SIZE]. Lemonade Submission Servers MUST NOT consider a supplied message size to be acceptable without expanding all BURL parts. A Lemonade capable client SHOULD use message size declaration. In particular the client MUST NOT send a message to a mail submission server, if it knows that the message exceeds the maximal message size advertised by the submission server. When including a message size in the MAIL FROM command, the client MUST use a value that is at least as large as the size of the assembled message data after resolution of all BURL parts. 4.5. Enhanced status code Support Lemonade compliant mail submission servers MUST support SMTP Service Extension for Returning Enhanced Error Codes [SMTP-STATUSCODES]. These allow a client to determine the precise cause of failure. 4.6. Encryption and Compression Lemonade Compliant mail submission servers MUST support SMTP Service Extension for Secure SMTP over TLS [SMTP-TLS]. Support for the DEFLATE compression method, as described in [TLS-COMP], is RECOMMENDED. Lemonade Submission Servers MUST support the QUICKSTART extension defined in $lt;No Draft>, which provides for considerably fewer round-trips at the commencement of a submission. Cridland, et al. Expires October 5, 2007 [Page 8] Internet-Draft Lemonade Profile April 2007 5. Lemonade Message Stores All Lemonade Message Stores implement Internet Message Access Protocol, as defined in [IMAP]. Therefore any MUA written to access messages using the facilities described in [IMAP] will interoperate with a Lemonade Message Store. In addition, Lemonade Message Stores provide a set of extensions to address the limitations of some clients and networks. 5.1. Quick resynchronization Resynchronization is a costly part of an IMAP session, and mobile networks are generally more prone to unintended disconnection, which in turns makes this problem more acute. Therefore Lemonade Message Stores provide a suite of extensions to reduce the synchronization cost. Lemonade Compliant IMAP servers MUST support the CONDSTORE [IMAP-CONDSTORE] and the QRESYNC [IMAP-QRESYNC] extensions. These allow a client to quickly resynchronize any mailbox by asking the server to return all flag changes and expunges that have occurred since a previously recorded state. This can also speed up client reconnect in case the transport layer is cut, whether accidentally or as part of a change in network. [IMAP-SYNC-HOWTO] details how clients perform efficient mailbox resynchronization. 5.2. Message part handling The handling of message parts, especially attachments, represents a set of challenges to limited devices, both in terms of the bandwidth used, and the capability of the device. Lemonade Compliant IMAP servers MUST support the BINARY [IMAP-BINARY] extension. This moves MIME body part decoding operations from the client to the server. The decoded data is always equal or less than the encoded representation, so this reduces bandwidth effectively. [IMAP-BINARY] allows for servers to refuse to accept uploaded messages containing binary data, by not accepting the Binary content- transfer-encoding; however Lemonade Compliant IMAP servers SHALL always accept binary encoded MIME messages in APPEND commands for any folder. [IMAP-CONVERT] MUST also be supported by servers, which allows clients to request conversions between media types, and allows for Cridland, et al. Expires October 5, 2007 [Page 9] Internet-Draft Lemonade Profile April 2007 scaling images, etc. This provides the ability to view attachments (and sometimes body parts) without the facility to cope with a wide range of media types, or to efficiently view attachments. 5.3. Compression The IETF has for some time generally agreed that compression is best handled at as low a level as possible, therefore Lemonade Message Stores SHOULD support the Deflate compression algorithm for TLS, as defined in [TLS-COMP]. However, the working group acknowledges that for many endpoints, this is a rarely deployed technology, and as such, Lemonade Message Stores MUST provide [IMAP-COMPRESS] support for fallback application-level stream compression, where TLS is not actively providing compression. 5.4. In band notifications Lemonade Message Stores MUST support the IDLE [IMAP-IDLE] extension. The extension allows clients to receive unsolicited notifications about changes in the selected mailbox, without needing to poll for changes. The responses forming these notifications MUST be sent in a timely manner when such changes happen. Lemonade Message Stores also provide the NOTIFY extension described in [IMAP-NOTIFY], which allows clients to request specific event types to be sent immediately to the client, both for the currently selected folder and others. Such event types include message delivery, and mailbox renames. 5.5. Searching and View Filters Lemonade Message Stores MUST support the ESEARCH [IMAP-ESEARCH] extension. The extension allows clients to efficiently find the first or last messages, find a count of matching messages, and obtain a list of matching messages in a considerably more compact representation. Lemonade Message Stores MUST support the WITHIN [IMAP-WITHIN] extension. The extension allows clients to easily find all messages that were delivered within a specific time period. Lemonade Message Stores also provide a mechanism for clients to avoid handling an entire mailbox, instead accessing a view of the mailbox. This technique, common in many desktop clients as a client-side capability, is useful for constrained clients to minimize the quantity of messages and notification data. Cridland, et al. Expires October 5, 2007 [Page 10] Internet-Draft Lemonade Profile April 2007 Lemonade Message Stores therefore MUST implement the CONTEXT extension defined in [IMAP-CONTEXT]. 5.6. Mailbox Handling Lemonade Message Stores MUST support the NAMESPACE [IMAP-NAMESPACE] extension. The extension allows clients to discover shared mailboxes and mailboxes belonging to other users, and provide a normalized heirarchy view of the mailboxes available. Lemonade Message Stores MUST support the METADATA [IMAP-METADATA] extension. This allows metadata to be stored against mailboxes, which is a facility used by other extensions mandated by this profile. Lemonade Message Stores MUST support the LIST-EXTENDED [IMAP-LISTEXT] extension. This is required for the METADATA [IMAP-METADATA] extension. It defines an extensible LIST command. 5.7. Forward Without Download In order to optimize network usage for the typical case where message content is copied to, or sourced from, the IMAP store, Lemonade provides support for a suite of extensions collectively known as Forward Without Download, discussed in detail in Section 7. Lemonade Message Stores MUST support CATENATE [IMAP-CATENATE], UIDPLUS [IMAP-UIDPLUS] and URLAUTH [IMAP-URLAUTH]. 5.8. Additional IMAP extensions Lemonade Message Stores MUST support the LITERAL+ [IMAP-LITERAL+] extension. The extension allows clients to save a round trip each time a non-synchronizing literal is sent. Lemonade Compliant IMAP servers MUST support IMAP over TLS [IMAP] as required by [IMAP]. As noted above in Section 5.3, servers SHOULD support the deflate compression algorithm for TLS, as specified in [TLS-COMP] 5.9. Registration of $Forwarded IMAP keyword The $Forwarded IMAP keyword is used by several IMAP clients to specify that the marked message was forwarded to another email address, embedded within or attached to a new message. A mail client sets this keyword when it successfully forwards the message to another email address. Typical usage of this keyword is to show a different (or additional) icon for a message that has been forwarded. Cridland, et al. Expires October 5, 2007 [Page 11] Internet-Draft Lemonade Profile April 2007 Once set the flag SHOULD NOT be cleared. Lemonade Message Stores MUST be able to store the $Forwarded keyword. They MUST preserve it on the COPY operation. The servers MUST support the SEARCH KEYWORD $Forwarded. 6. Lemonade Mail User Agents Although all existing IMAP MUAs are Lemonade compliant in as much as all Lemonade services are based on the existing [IMAP] and [SUBMIT] protocols, client implementors are encouraged to take full advantage of the facilities provided by Lemonade Submission Servers and Lemonade Message Stores, as described in Section 4 and Section 5 respectively. Note that the explicit usage of [SUBMIT] means that when opening a connection to the submission server, clients MUST do so using port 587 unless explicitly configured to use an alternate port. If the TCP connection to the submission server fails to open using port 587, the client MAY then immediately retry using a different port, such as 25. See [SUBMIT] information on why using port 25 is likely to fail depending on the current location of the client, and may result in a failure code during the SMTP transaction. In addition, some specifications are useful to support interoperable messaging with an enhanced user experience. Lemonade capable clients SHOULD support the Format and DelSp parameters to the text/plain media type described in [FLOWED], and generate this format for messages. Lemonade capable clients SHOULD support, and use, the $Forwarded keyword described in Section 5.9. 7. Forward without download 7.1. Motivations The advent of client/server email using the [IMAP] and [SUBMIT] protocols changed what formerly were local disk operations to become repetitive network data transmissions. Lemonade "forward without download" makes use of the [SMTP-BURL] extension to enable access to external sources during the submission of a message. In combination with the [IMAP-URLAUTH] extension, inclusion of message parts or even entire messages from the IMAP mail Cridland, et al. Expires October 5, 2007 [Page 12] Internet-Draft Lemonade Profile April 2007 store is possible with a minimal trust relationship between the IMAP and SMTP SUBMIT servers. Lemonade "forward without download" has the advantage of maintaining one submission protocol, and thus avoids the risk of having multiple parallel and possibly divergent mechanisms for submission. The client can use [SUBMIT] extensions without these being added to IMAP. Furthermore, by keeping the details of message submission in the SMTP SUBMIT server, Lemonade "forward without download" can work with other message retrieval protocols such as POP, NNTP, or whatever else may be designed in the future. 7.2. Message Sending Overview The act of sending an email message can be thought of as involving multiple steps: initiation of a new draft, draft editing, message assembly, and message submission. Initiation of a new draft and draft editing takes place in the MUA. Frequently, users choose to save more complex messages on an [IMAP] server (via the APPEND command with the \Draft flag) for later recall by the MUA and resumption of the editing process. Message assembly is the process of producing a complete message from the final revision of the draft and external sources. At assembly time, external data is retrieved and inserted in the message. Message submission is the process of inserting the assembled message into the [ESMTP] infrastructure, typically using the [SUBMIT] protocol. 7.3. Traditional Strategy Traditionally, messages are initiated, edited, and assembled entirely within an MUA, although drafts may be saved to an [IMAP] server and later retrieved from the server. The completed text is then transmitted to an MSA for delivery. There is often no clear boundary between the editing and assembly process. If a message is forwarded, its content is often retrieved immediately and inserted into the message text. Similarly, when external content is inserted or attached, the content is usually retrieved immediately and made part of the draft. As a consequence, each save of a draft and subsequent retrieve of the draft transmits that entire (possibly large) content, as does message submission. Cridland, et al. Expires October 5, 2007 [Page 13] Internet-Draft Lemonade Profile April 2007 In the past, this was not much of a problem, because drafts, external data, and the message submission mechanism were typically located on the same system as the MUA. The most common problem was running out of disk quota. 7.4. Step by step description The model distinguishes between a Messaging User Agent (MUA), an IMAPv4Rev1 Server ([IMAP]) and a SMTP submit server ([SUBMIT]), as illustrated in Figure 1. +--------------------+ +--------------+ | | <------------ | | | MUA (M) | | IMAPv4Rev1 | | | | Server | | | ------------> | (Server I) | +--------------------+ +--------------+ ^ | ^ | | | | | | | | | | | | | | | | | | | | | | | | v | | +--------------+ | |----------------------> | SMTP | | | Submit | |-----------------------------| Server | | (Server S) | +--------------+ Figure 1: Lemonade "forward without download" Lemonade "forward without download" allows a Messaging User Agent to compose and forward an e-mail combining fragments that are located in an IMAP server, without having to download these fragments to the client. There are two ways to perform "forward without download" based on where the message assembly takes place. The first uses extended APPEND command [IMAP-CATENATE] to edit a draft message in the message store and cause the message assembly on the IMAP server. This is most often used when a copy of the message is to be retained on the IMAP server, as discussed in Section 7.6. The second uses a succession of BURL and BDAT commands to submit and assemble through concatenation, message data from the client and external data fetched from the provided URL. The two subsequent Cridland, et al. Expires October 5, 2007 [Page 14] Internet-Draft Lemonade Profile April 2007 sections provide step-by-step instructions on how "forward without download" is achieved. 7.4.1. Message assembly using IMAP CATENATE extension In the [SMTP-BURL]/[IMAP-CATENATE] variant of the Lemonade "forward without download" strategy, messages are initially composed and edited within an MUA. The [IMAP-CATENATE] extension to [IMAP] is then used to create the messages on the IMAP server by transmitting new text and assembling them. The UIDPLUS [IMAP-UIDPLUS] IMAP extension is used by the client in order to learn the UID of the created messages. Finally a [IMAP-URLAUTH] format URL is given to a [SUBMIT] server for submission using the BURL [SMTP-BURL] extension. The flow involved to support such a use case consists of: M: {to I -- Optional} The client connects to the IMAP server, optionally starts TLS (if data confidentiality is required), authenticates, opens a mailbox ("INBOX" in the example below) and fetches body structures (See [IMAP]). Example: M: A0051 UID FETCH 25627 (UID BODYSTRUCTURE) I: * 161 FETCH (UID 25627 BODYSTRUCTURE (("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152 23)( "TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "trip.txt") "<960723163407.20117h@washington.example.com>" "Your trip details" "BASE64" 4554 73) "MIXED")) I: A0051 OK completed M: {to I} The client invokes CATENATE (See [IMAP-CATENATE] for details of the semantics and steps) -- this allows the MUA to create messages on the IMAP server using new data combined with one or more message parts already present on the IMAP server. Note that the example for this step doesn't use the LITERAL+ [IMAP-LITERAL+] extension. Without LITERAL+ the new message is constructed using 3 round-trips. If LITERAL+ is used, the new message can be constructed using one round-trip. Cridland, et al. Expires October 5, 2007 [Page 15] Internet-Draft Lemonade Profile April 2007 M: A0052 APPEND Sent FLAGS (\Draft \Seen $MDNSent) CATENATE (TEXT {475} I: + Ready for literal data M: Message-ID: <419399E1.6000505@caernarfon.example.org> M: Date: Thu, 12 Nov 2004 16:57:05 +0000 M: From: Bob Ar M: MIME-Version: 1.0 M: To: foo@example.net M: Subject: About our holiday trip M: Content-Type: multipart/mixed; M: boundary="------------030308070208000400050907" M: M: --------------030308070208000400050907 M: Content-Type: text/plain; format=flowed M: M: Our travel agent has sent the updated schedule. M: M: Cheers, M: Bob M: --------------030308070208000400050907 M: URL "/INBOX;UIDVALIDITY=385759045/; UID=25627/;Section=2.MIME" URL "/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2" TEXT {44} I: + Ready for literal data M: M: --------------030308070208000400050907-- M: ) I: A0052 OK [APPENDUID 387899045 45] CATENATE Completed M: {to I} The client uses GENURLAUTH command to request a URLAUTH URL (See [IMAP-URLAUTH]). I: {to M} The IMAP server returns a URLAUTH URL suitable for later retrieval with URLFETCH (See [IMAP-URLAUTH] for details of the semantics and steps). M: A0054 GENURLAUTH "imap://bob.ar@example.org/Sent; UIDVALIDITY=387899045/;uid=45;expire=2005-10- 28T23:59:59Z;urlauth=submit+bob.ar" INTERNAL I: * GENURLAUTH "imap://bob.ar@example.org/Sent; UIDVALIDITY=387899045/;uid=45;expire= 2005-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:91354a473744909de610943775f92038" I: A0054 OK GENURLAUTH completed M: {to S} The client connects to the mail submission server and starts a new mail transaction. It uses BURL to let the SMTP submit server fetch the content of the message from the IMAP server (See [IMAP-URLAUTH] for details of the semantics and steps -- this allows Cridland, et al. Expires October 5, 2007 [Page 16] Internet-Draft Lemonade Profile April 2007 the MUA to authorize the SMTP submit server to access the message composed as a result of the CATENATE step). Note that the second EHLO command is required after a successful STARTTLS command. Also note that there might be a third required EHLO command if the second EHLO response doesn't list any BURL options. Section 7.4.2 demonstrates this. S: 220 owlry.example.org ESMTP M: EHLO potter.example.org S: 250-owlry.example.com S: 250-8BITMIME S: 250-BINARYMIME S: 250-PIPELINING S: 250-BURL imap S: 250-CHUNKING S: 250-AUTH PLAIN S: 250-DSN S: 250-SIZE 10240000 S: 250-STARTTLS S: 250 ENHANCEDSTATUSCODES M: STARTTLS S: 220 Ready to start TLS ...TLS negotiation, subsequent data is encrypted... M: EHLO potter.example.org S: 250-owlry.example.com S: 250-8BITMIME S: 250-BINARYMIME S: 250-PIPELINING S: 250-BURL imap S: 250-CHUNKING S: 250-AUTH PLAIN S: 250-DSN S: 250-SIZE 10240000 S: 250 ENHANCEDSTATUSCODES M: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8= S: 235 2.7.0 PLAIN authentication successful. M: MAIL FROM: S: 250 2.5.0 Address Ok. M: RCPT TO: S: 250 2.1.5 foo@example.net OK. M: BURL imap://bob.ar@example.org/Sent;UIDVALIDITY=387899045/; uid=45/;urlauth=submit+bar:internal: 91354a473744909de610943775f92038 LAST S: {to I} The mail submission server uses URLFETCH to fetch the message to be sent (See [IMAP-URLAUTH] for details of the semantics and steps. The so-called "pawn-ticket" authorization mechanism uses a URI which contains its own authorization credentials.). Cridland, et al. Expires October 5, 2007 [Page 17] Internet-Draft Lemonade Profile April 2007 I: {to S} Provides the message composed as a result of the CATENATE step). Mail submission server opens IMAP connection to the IMAP server: I: * OK [CAPABILITY IMAP4REV1 STARTTLS NAMESPACE LITERAL+ CATENATE URLAUTH UIDPLUS CONDSTORE IDLE] imap.example.com IMAP server ready S: a000 STARTTLS I: a000 Start TLS negotiation now ...TLS negotiation, if successful - subsequent data is encrypted... S: a001 LOGIN submitserver secret I: a001 OK submitserver logged in S: a002 URLFETCH "imap://bob.ar@example.org/Sent; UIDVALIDITY=387899045/;uid=45/;urlauth=submit+bob.ar: internal:91354a473744909de610943775f92038" I: * URLFETCH "imap://bob.ar@example.org/Sent; UIDVALIDITY=387899045/;uid=45/;urlauth=submit+bob.ar: internal:91354a473744909de610943775f92038" {15065} ...message body follows... S: a002 OK URLFETCH completed I: a003 LOGOUT S: * BYE See you later S: a003 OK Logout successful Note that if the IMAP server doesn't send CAPABILITY response code in the greeting, the mail submission server must issue the CAPABILITY command to learn about supported IMAP extensions as described in [IMAP]. Also, if data confidentiality is not required the mail submission server may omit the STARTTLS command before issuing the LOGIN command. S: {to M} Submission server assembles the complete message and if the assembly succeeds it returns OK to the MUA: S: 250 2.5.0 Ok. M: {to I} The client marks the message containing the forwarded attachment on the IMAP server. M: A0053 UID STORE 25627 +FLAGS.SILENT ($Forwarded) I: * 215 FETCH (UID 25627 MODSEQ (12121231000)) I: A0053 OK STORE completed Note: the UID STORE command shown above will only work if the marked Cridland, et al. Expires October 5, 2007 [Page 18] Internet-Draft Lemonade Profile April 2007 message is in the currently selected mailbox; otherwise, it requires a SELECT. This command can be omitted, as it simply changes non- operational metadata not essential to client operations or interoperability. The untagged FETCH response is due to [IMAP-CONDSTORE]. The $Forwarded IMAP keyword is described in Section 5.9. 7.4.2. Message assembly using SMTP CHUNKING and BURL extensions In the [IMAP-URLAUTH]/[SMTP-BURL] variant of the Lemonade "forward without download" strategy, messages are initially composed and edited within an MUA. During submission [SUBMIT], BURL [SMTP-BURL] and BDAT [SMTP-BINARYMIME] commands are used to create the messages from multiple parts. New body parts are supplied using BDAT commands, while existing body parts are referenced using [IMAP-URLAUTH] format URLs in BURL commands. The flow involved to support such a use case consists of: M: {to I -- Optional} The client connects to the IMAP server, optionally starts TLS (if data confidentiality is required), authenticates, opens a mailbox ("INBOX" in the example below) and fetches body structures (See [IMAP]). Example: M: A0051 UID FETCH 25627 (UID BODYSTRUCTURE) I: * 161 FETCH (UID 25627 BODYSTRUCTURE (("TEXT" "PLAIN" ("CHARSET" "US-ASCII") NIL NIL "7BIT" 1152 23)( "TEXT" "PLAIN" ("CHARSET" "US-ASCII" "NAME" "trip.txt") "<960723163407.20117h@washington.example.com>" "Your trip details" "BASE64" 4554 73) "MIXED")) I: A0051 OK completed M: {to I} The client uses GENURLAUTH command to request URLAUTH URLs (See [IMAP-URLAUTH]) referencing pieces of the message to be assembled. I: {to M} The IMAP server returns URLAUTH URLs suitable for later retrieval with URLFETCH (See [IMAP-URLAUTH] for details of the semantics and steps). Cridland, et al. Expires October 5, 2007 [Page 19] Internet-Draft Lemonade Profile April 2007 M: A0054 GENURLAUTH "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar" INTERNAL "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar" INTERNAL I: * GENURLAUTH "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:A0DEAD473744909de610943775f9BEEF" "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:BEEFA0DEAD473744909de610943775f9" I: A0054 OK GENURLAUTH completed M: {to S} The client connects to the mail submission server and starts a new mail transaction. It uses BURL to instruct the SMTP submit server to fetch from the IMAP server pieces of the message to be sent (See [SMTP-BURL] for details of the semantics and steps). Note that the second EHLO command is required after a successful STARTTLS command. The third EHLO command is required if and only if the second EHLO response doesn't list any BURL options. See Section 7.4.1 for an example of submission where the third EHLO command/response is not present. S: 220 owlry.example.org ESMTP M: EHLO potter.example.org S: 250-owlry.example.com S: 250-8BITMIME S: 250-BINARYMIME S: 250-PIPELINING S: 250-BURL S: 250-CHUNKING S: 250-AUTH DIGEST-MD5 S: 250-DSN S: 250-SIZE 10240000 S: 250-STARTTLS S: 250 ENHANCEDSTATUSCODES M: STARTTLS S: 220 Ready to start TLS ...TLS negotiation, subsequent data is encrypted... M: EHLO potter.example.org S: 250-owlry.example.com S: 250-8BITMIME S: 250-BINARYMIME S: 250-PIPELINING Cridland, et al. Expires October 5, 2007 [Page 20] Internet-Draft Lemonade Profile April 2007 S: 250-BURL S: 250-CHUNKING S: 250-AUTH DIGEST-MD5 CRAM-MD5 PLAIN EXTERNAL S: 250-DSN S: 250-SIZE 10240000 S: 250 ENHANCEDSTATUSCODES M: AUTH PLAIN aGFycnkAaGFycnkAYWNjaW8= S: 235 2.7.0 PLAIN authentication successful. M: EHLO potter.example.org S: 250-owlry.example.com S: 250-8BITMIME S: 250-BINARYMIME S: 250-PIPELINING S: 250-BURL imap imap://imap.example.org S: 250-CHUNKING S: 250-AUTH DIGEST-MD5 CRAM-MD5 PLAIN EXTERNAL S: 250-DSN S: 250-SIZE 10240000 S: 250 ENHANCEDSTATUSCODES M: MAIL FROM: BODY=BINARY S: 250 2.5.0 Address Ok. M: RCPT TO: S: 250 2.1.5 foo@example.net OK. M: BDAT 475 M: Message-ID: <419399E1.6000505@caernarfon.example.org> M: Date: Thu, 12 Nov 2004 16:57:05 +0000 M: From: Bob Ar M: MIME-Version: 1.0 M: To: foo@example.net M: Subject: About our holiday trip M: Content-Type: multipart/mixed; M: boundary="------------030308070208000400050907" M: M: --------------030308070208000400050907 M: Content-Type: text/plain; format=flowed M: M: Our travel agent has sent the updated schedule. M: M: Cheers, M: Bob M: --------------030308070208000400050907 S: 250 2.5.0 OK M: BURL imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:A0DEAD473744909de610943775f9BEEF S: 250 2.5.0 OK M: BURL imap://bob.ar@example.org/INBOX; Cridland, et al. Expires October 5, 2007 [Page 21] Internet-Draft Lemonade Profile April 2007 UIDVALIDITY=385759045/;UID=25627/;Section=2; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:BEEFA0DEAD473744909de610943775f9 S: 250 2.5.0 OK M: BDAT 44 LAST M: M: --------------030308070208000400050907-- S: {to I} The mail submission server uses URLFETCH to fetch the pieces of the message to be sent (See [SMTP-BURL] for details of the semantics and steps. The so-called "pawn-ticket" authorization mechanism uses a URI which contains its own authorization credentials.). I: {to S} Returns the requested body parts. Mail submission server opens IMAP connection to the IMAP server: I: * OK [CAPABILITY IMAP4REV1 STARTTLS NAMESPACE LITERAL+ CATENATE URLAUTH UIDPLUS CONDSTORE IDLE] imap.example.com IMAP server ready S: a001 LOGIN submitserver secret I: a001 OK submitserver logged in S: a002 URLFETCH "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:A0DEAD473744909de610943775f9BEEF" "imap:// bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:BEEFA0DEAD473744909de610943775f9" I: * URLFETCH "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2.MIME; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:A0DEAD473744909de610943775f9BEEF" {84} ...message section follows... "imap://bob.ar@example.org/INBOX; UIDVALIDITY=385759045/;UID=25627/;Section=2; expire=2006-10-28T23:59:59Z;urlauth=submit+bob.ar: internal:BEEFA0DEAD473744909de610943775f9" {15065} ...message section follows... S: a002 OK URLFETCH completed I: a003 LOGOUT S: * BYE See you later S: a003 OK Logout successful Note that if the IMAP server doesn't send CAPABILITY response code in the greeting, the mail submission server must issue the CAPABILITY command to learn about supported IMAP extensions as described in Cridland, et al. Expires October 5, 2007 [Page 22] Internet-Draft Lemonade Profile April 2007 [IMAP]. Also, if data confidentiality is required the mail submission server should start TLS before issuing the LOGIN command. S: {to M} Submission server assembles the complete message and if the assembly succeeds it acknowledges acceptance of the message by sending 250 response to the last BDAT command: S: 250 2.5.0 Ok, message accepted. M: {to I} The client marks the message containing the forwarded attachment on the IMAP server. M: A0053 UID STORE 25627 +FLAGS.SILENT ($Forwarded) I: * 215 FETCH (UID 25627 MODSEQ (12121231000)) I: A0053 OK STORE completed Note: the UID STORE command shown above will only work if the marked message is in the currently selected mailbox; otherwise, it requires a SELECT. As in the previous example, this command is not critical, and can be omitted. The untagged FETCH response is due to [IMAP-CONDSTORE]. The $Forwarded IMAP keyword is described in Section 5.9. 7.5. Security Considerations for pawn-tickets. The so-called "pawn-ticket" authorization mechanism uses a URI, which contains its own authorization credentials using [IMAP-URLAUTH]. The advantage of this mechanism is that the SMTP submit [SUBMIT] server cannot access any data on the [IMAP-URLAUTH] server without a "pawn- ticket" created by the client. The "pawn-ticket" grants access only to the specific data that the SMTP submit [SUBMIT] server is authorized to access, can be revoked by the client, and can have a time-limited validity. 7.6. Copies of Sent messages: The fcc problem The "fcc problem" refers to delivering a copy of a message to a mailbox, or "file carbon copy". By far, the most common case of fcc is a client leaving a copy of outgoing mail in a "Sent Mail" or "Outbox" mailbox. In the traditional strategy, the MUA duplicates the effort spent in transmitting to the MSA by writing the message to the fcc destination in a separate step. This may be a write to a local disk file or an APPEND to a mailbox on an IMAP server. The latter is one of the Cridland, et al. Expires October 5, 2007 [Page 23] Internet-Draft Lemonade Profile April 2007 "repetitive network data transmissions" which represents the "problem" aspect of the "fcc problem". The BURL [SMTP-BURL] extension can be used to eliminate the additional transmission. The final message is uploaded to the mailbox designed for outgoing mail, by the APPEND command of [IMAP]. Note that APPEND, including when enhanced by [IMAP-CATENATE], can only create a single copy of the message and this is only of use on the server which stages the outgoing message for submission. Additional copies of the message on the same server can be created by using one or more COPY commands. 8. OMA MEM Requirement document The OMA MEM activity has collected a set of use cases and derived requirements for a mobile email enabler (MEM). The resulting work is summarized in OMA MEM Requirement document [MEM-req]. Some requirements relate to email protocols, some involve other OMA technologies outside the scope of IETF and some relate to implementations and normative interoperability statements for clients and servers. 8.1. OMA MEM Architecture The OMA MEM activity has derived a logical architecture from the requirements and use cases described in [MEM-req]. The logical architecture, its elements and interfaces and the notations that it uses can be found in [MEM-arch]. 8.2. OMA MEM Deployment Issues The OMA MEM Architecture document [MEM-arch] further identifies deployment models. Certain of these deployment models are not what IETF has conventionally modeled. They require special attention to end-to-end security aspects and may warrant introduction of additional security measures (e.g. object level encryption). 8.3. OMA MEM proxy The OMA MEM Architecture document [MEM-arch] identifies OMA MEM server proxies as server components that may be deployed. Both IMAP and SMTP generally are compatible with proxies between the client and the server. Such proxies may disrupt end-to-end encryption, with the transport-level encryption ending at the proxy Cridland, et al. Expires October 5, 2007 [Page 24] Internet-Draft Lemonade Profile April 2007 and re-generating from the proxy to the server. Again this may require additional security measures like object level encryption, and this mode of operation is not recommended. 8.4. IETF Lemonade Architecture This section gives a brief introduction to the Lemonade Architecture. The IETF Lemonade activity has derived a profile with the logical architecture represented in Figure 15, where arrows indicate content flows. ______________ | | _________| Notification | | | Mechanism | | |______________| |Notif. ^ |Protocol | | ___|______ | | | _____ __v__ IMAP | Lemonade | ESMTP | | | |<----------->| IMAP |<---------------| MTA | | MUA |- | Store | |_____| |_____| \ |__________| \ | \ |URLAUTH \SUBMIT | \ ____v_____ \ | | _____ \ | Lemonade | ESMTP | | ---->| Submit |--------------->| MTA | | Server | |_____| |__________| Figure 15: Lemonade logical architecture The Lemonade profile assumes: <> o IMAP protocol [IMAP] including Lemonade profile extensions o Submit protocol ([SUBMIT], profile of [ESMTP]) including Lemonade profile extensions o Lemonade profile compliant IMAP store connected to MTA (Mail Transfer Agent) via ESMTP [ESMTP]. o Lemonade profile compliant Submit server connected to MTA via ESMTP Cridland, et al. Expires October 5, 2007 [Page 25] Internet-Draft Lemonade Profile April 2007 o Lemonade profile message store / Submit server protocols (URLAUTH) (see [IMAP-URLAUTH]). o Outband server to client notifications relying on external notification mechanisms (and notification protocols) that may be out of scope of the Lemonade profile. o A Lemonade aware MUA (Mail User Agent). While use of outband notification is described in the Lemonade profile, support for the underlying notifications mechanisms/protocols is out of scope of the Lemonade specifications. Note that in Figure 15 the IMAP server and Submit server are represented connected to MTAs (Mail Transfer Agents) via [ESMTP]. This is not really essential. It could as well be X.400 so long as the message in the store is in the internet form. OMA MEM identifies other functionalities. These are considered as out of scope of the Lemonade work and will need to be specified by OMA MEM. 8.5. Lemonade profile logical architecture This section details the Lemonade profile logical architecture. This architecture is also expected to support the OMA MEM logical Architecture. 8.5.1. Relationship between the OMA MEM and Lemonade logical architectures Figure 16 illustrates the mapping of the IETF Lemonade logical architecture on the OMA MEM logical architecture. Cridland, et al. Expires October 5, 2007 [Page 26] Internet-Draft Lemonade Profile April 2007 _____________________ | Other_Mob. Enablers | | |--------------| | _________| Notification | | | | | Mechanism | | | | |______________| | |Notif. |____________^________| |Protocol ______|__________ ME-4 | | ___|_ME-3_ | ___|____ | | | | _____ | __v__ | IMAP | | Lemonade | | ESMTP | | || |<----------->| IMAP |<-----------| MTA | || MUA || ME-2a | | Store | | |_____| ||_____||\ME-1 | |__________| | | MEM | \ | | | | Client| \ | |URLAUTH | |_______| \SUBMIT | | \ | ____v_____ | \ | | | | _____ \ | | Lemonade | | ESMTP | | ---->| Submit |----------->| MTA | ME-2b | | Server | | |_____| | |__________| | |MEM Email | |Server Server| |_________________| ^ |ME-5 | Figure 16: Mapping of Lemonade profile logical architecture onto the OMA MEM logical architecture. As described in Section 8.4, the Lemonade profile assumes Lemonade profile compliant IMAP stores and Submit servers. Because the Lemonade profile extends the IMAP store and the submit server, the mobile enablement of email provided by the Lemonade profile is directly provided in these server. Mapped to OMA MEM logical architecture, for the case considered and specified by the Lemonade profile, the MEM server and email server logically combined. They are however split into distinct Lemonade message store and Lemonade submit server. The OMA MEM interfaces ME-2 ([MEM-arch]) consists of two interfaces ME-2a and ME-2b associated respectively to IMAP extended according to the Lemonade profile and SUBMIT extended according to the Lemonade profile. The MUA is part of the MEM client. Cridland, et al. Expires October 5, 2007 [Page 27] Internet-Draft Lemonade Profile April 2007 External notifications mechanism can be part of the other OMA enabler specified by OMA (or other activities). 8.5.2. Lemonade realization of OMA MEM with non-Lemonade compliant servers The OMA MEM activity is not limited to enabling Lemonade compliant servers. It explicitly identifies the need to support other backends. 8.5.2.1. Lemonade realization of OMA MEM with non-Lemonade enhanced IMAP servers Figure 17 illustrates the case of IMAP servers that are not (yet) Lemonade compliant / enhanced with Lemonade. In such case, the I2 interface between the MEM server components and the IMAP store and submit server are IMAP and SUBMIT. ______________ | | _________| Notification | | | Mechanism | | |______________| |Notif. ^ |Protocol | | ___|______ _____________ | | Lemonade | | | _____ __v__ IMAP | MEM | IMAP |NON-Lemonade | ESMTP | | | |<--------->|Enabler |<------>|IMAP |<----->| MTA | | MUA |\ ME-2a | Server | |Store | |_____| |_____| \ |__________| |_____________| \ | \ |URLAUTH \SUBMIT | \ ____v_____ _____________ \ | | | | _____ \ | Lemonade | SUBMIT |NON-Lemonade | ESMTP | | -->| MEM | |Submit | | | | Enabler |------->|Server |------>| MTA | ME-2b | Server | | | |_____| |__________| |_____________| Figure 17: Architecture to support non-Lemonade enhanced IMAP servers with a Lemonade realization of OMA MEM enabler. In Figure 17, the server may be a separate proxy. Cridland, et al. Expires October 5, 2007 [Page 28] Internet-Draft Lemonade Profile April 2007 8.5.2.2. Lemonade realization of OMA MEM with non-IMAP servers < Figure 18 illustrates the cases where the message store and submit servers are not IMAP store or submit servers. They may be POP3 servers or other proprietary message stores. ______________ | | _________| Notification | | | Mechanism | | |______________| |Notif. ^ |Protocol | | ___|______ _____________ | | Lemonade | | | _____ __v__ IMAP | MEM | I2 |Proprietary | ESMTP | | | |<--------->|Enabler |<------>|Message |<----->| MTA | | MUA |\ ME-2a | Server | |Store | |_____| |_____| \ |__________| |_____________| \ | \ |URLAUTH \SUBMIT | \ ____v_____ _____________ \ | | | | _____ \ | Lemonade | I2 |Proprietary | ESMTP | | -->| MEM | |Submit | | | | Enabler |------->|Server |------>| MTA | ME-2b | Server | | | |_____| |__________| |_____________| Figure 18: Architecture to support non-IMAP servers with a Lemonade realization of OMA MEM enabler. I2 designates proprietary adapters to the backends. They may involved functions performed in the message stores or submit server as well as in the MEM enabler server. In Figure 18, the server may be a separate proxy. 8.6. Filters and server to client notifications and Lemonade OMA MEM RD [MEM-req] and AD [MEM-arch] emphasize the need to provide mechanisms for server to client notifications of email events and filtering. Figure 19 illustrates how notification and filterings are Cridland, et al. Expires October 5, 2007 [Page 29] Internet-Draft Lemonade Profile April 2007 introduced in Lemonade profile. ______________ | | _________| Notification | | | Mechanism | | |______________| |Notif. ^ |Protocol -------\ _|_ | ______| ___\>|NF|____ | | | ---- | _____ __v__| IMAP |__ Lemonade |___ ESMTP __| | | |<-------->|VF| IMAP |DF |<--------|AF| MTA | | MUA |\ ME-2a |-- Store |--- --|_____| |_____| \ |_____________| ^ \_\_______________|_______| \ |URLAUTH \SUBMIT | \ ____v_____ \ | | _____ \ | Lemonade | ESMTP | | ---->| Submit |--------------->| MTA | ME-2b | Server | |_____| |__________| Figure 19: Filtering mechanism defined in Lemonade architecture In Figure 19, four categories of filters are defined: o AF: Administrative Filters - Set up by email service provider. AF are typically not configured by the user and set to apply policies content filtering, virus protection, spam filtering etc... o DF: Deposit Filters - Filters that are executed on deposit of new email messages. They can be defined as [SIEVE]. They can include vacation notices. o VF: View Filters - Filters that define which emails are visible to the MUA. View filters can be performed via IMAP using the facilities described in Section 5.5. o NF: Notification Filters - Filters that define for what email server events a notification is sent to the client, as described in Section 5.4. The filters are manageable from the MUA: o NF and DF: via SIEVE Management protocol [MANAGESIEVE] Cridland, et al. Expires October 5, 2007 [Page 30] Internet-Draft Lemonade Profile April 2007 o VF: via extended IMAP SEARCH commands discussed in Section 5.5. 9. Deployment Considerations Deployment considerations are discussed extensively in [LEMONADE-DEPLOYMENTS]. 10. Security Considerations Implementors are advised to examine the Security Considerations of all the referenced documents. This section merely highlights these, and advises implementors on specific issues relating to the combination of extensions. Security considerations on Lemonade "forward without download" are discussed throughout Section 7. Additional security considerations can be found in [IMAP] and other documents describing other SMTP and IMAP extensions comprising the Lemonade Profile. Note that the mandatory-to-implement authentication mechanism for SMTP submission is described in [SMTP-AUTH]. The mandatory-to- implement authentication mechanism for IMAP is described in [IMAP]. 10.1. Confidentiality Protection of Submitted Messages When clients submit new messages, link protection such as TLS guards against an eavesdropper seeing the contents of the submitted message. It is worth noting, however, that even if TLS is not used, the security risks are no worse if BURL is used to reference the text than if the text is submitted directly. If BURL is not used, an eavesdropper gains access to the full text of the message. If BURL is used, the eavesdropper may or may not be able to gain such access, depending on the form of BURL used. For example, some forms restrict use of the URL to an entity authorized as a submission server or a specific user. 10.2. TLS When Lemonade clients use the BURL extension to mail submission, an extension that requires sending a URLAUTH token to the mail submission server, such a token should be protected from interception to avoid a replay attack that may disclose the contents of the message to an attacker. TLS based encryption of the mail submission path will provide protection against this attack. Lemonade clients SHOULD use TLS-protected IMAP and mail submission Cridland, et al. Expires October 5, 2007 [Page 31] Internet-Draft Lemonade Profile April 2007 channels when using BURL-based message submission to protect the URLAUTH token from interception. Lemonade compliant mail submission servers SHOULD use TLS-protected IMAP connections when fetching message content using the URLAUTH token provided by the Lemonade client. When a client uses SMTP STARTTLS to send a BURL command which references non-public information, there is a user expectation that the entire message content will be treated confidentially. To meet this expectation, the message submission server should use STARTTLS or a mechanism providing equivalent data confidentiality when fetching the content referenced by that URL. 10.3. Additional extensions and deployment models This specification provides no additional security measures beyond those in the referenced Internet Mail and Lemonade documents. We note however the security risks associated to: o Outband notifications o Server configuration by client o Client configuration by server o Presence of proxy servers o Presence of servers as intermediaries o In general the deployment models considered by OMA MEM that are not conventional IETF deployment models. o Measures to address a perceived need to traverse firewalls and mobile network intermediaries. 11. IANA considerations This document does not require any IANA registration or action that are not covered by the different drafts and RFCs included in the realization described in this document. 12. Version history o Version 04: * Major reorganization of text. * Move checklist summary to beginning of document, collate Submission and Store server requirements. o Version 03: * Replaced RECONNECT (server side quick reconned) with QRESYNC (client side quick reconnect) Cridland, et al. Expires October 5, 2007 [Page 32] Internet-Draft Lemonade Profile April 2007 * Added WITHIN and LIST-EXTENDED. * Moved IDLE extension to a separate section. * Added requirement for clients to use Format=flowed. o Version 02: * Update of references and how they are displayed in the text (Comments from Randy Gellens) * Update of list of extensions to support as MUST by the Lemonade Profile Bis * Update of options for compression via placeholder imap- compression section describing compression requirements * Update of support of TCP chalenged environments * Update of support of object level encryption * Clarified the use of $Forwarded in the examples, and demonstrated how to remove the \Draft flag from the sent message * Clarified $Forwarded * Added RECONNECT to imap-condstore section * Add new section imap-bodypart, "Message part handling", describing BINARY and CONVERT requirements * Added placeholder section for notifications * Added various extensions to imap-other section, and added clarifying comments to IDLE, NAMESPACE, and a further references to TLS DEFLATE compression * Added extension names to IMAP table * Fixed all issues found with original Lemonade profile so far. o Version 01: * Lemonade profile has been introduced in-line, with some updates / corrections. * Subsequent re-organization of the text * Details of extensions proper to Lemonade Profile-bis have been updated to refer to the drafts newly accepted as WG IETF drafts. * Addition of appendix on attachements streaming. o Version 00: * It evolved from a combination of the content of Lemonade profile and the OMA MEM realization internet draft. 13. Acknowledgements The editors acknowledge and appreciate the work and comments of the IETF Lemonade working group and the OMA MEM working group. In particular, the editors would like to thank Eric Burger, Randall Gellens, Zoltan Ordogh, Greg Vaudreuil, and Fan Xiaohui for their comments and reviews. Cridland, et al. Expires October 5, 2007 [Page 33] Internet-Draft Lemonade Profile April 2007 14. References 14.1. Normative References [FLOWED] Gellens, R., "The Text/Plain Format and DelSp Parameters", RFC 3676, February 2004. [IMAP] Crispin, M., "INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1", RFC 3501, March 2003. [IMAP-BINARY] Nerenberg, L., "IMAP4 Binary Content Extension", RFC 3516, April 2003. [IMAP-CATENATE] Resnick, P., "Internet Message Access Protocol (IMAP) CATENATE Extension", RFC 4469, April 2006. [IMAP-COMPRESS] Gulbrandsen, A., "The IMAP COMPRESS Extension", draft-ietf-lemonade-compress-07 (work in progress), January 2007. [IMAP-CONDSTORE] Melnikov, A. and S. Hole, "IMAP Extension for Conditional STORE Operation or Quick Flag Changes Resynchronization", RFC 4551, June 2006. [IMAP-CONTEXT] Cridland, D. and C. King, "Contexts for IMAP4", draft-cridland-imap-context-00 (work in progress), October 2006. [IMAP-CONVERT] Maes, S. and R. Cromwell, "CONVERT", draft-ietf-lemonade-convert-05 (work in progress), October 2006. [IMAP-ESEARCH] Melnikov, A. and D. Cridland, "IMAP4 Extension to SEARCH Command for Controlling What Kind of Information Is Returned", RFC 4731, November 2006. [IMAP-IDLE] Leiba, B., "IMAP4 IDLE command", RFC 2177, June 1997. [IMAP-LISTEXT] Leiba, B. and A. Melnikov, "IMAP4 LIST Command Cridland, et al. Expires October 5, 2007 [Page 34] Internet-Draft Lemonade Profile April 2007 Extensions", draft-ietf-imapext-list-extensions-18 (work in progress), September 2006. [IMAP-LITERAL+] Myers, J., "IMAP4 non-synchronizing literals", RFC 2088, January 1997. [IMAP-METADATA] Daboo, C., "IMAP METADATA Extension", draft-daboo-imap-annotatemore-11 (work in progress), February 2007. [IMAP-NAMESPACE] Gahrns, M. and C. Newman, "IMAP4 Namespace", RFC 2342, May 1998. [IMAP-NOTIFY] King, C., "The IMAP NOTIFY Extension", draft-gulbrandsen-imap-notify-03 (work in progress), March 2007. [IMAP-QRESYNC] Melnikov, A., "IMAP4 Extensions for Quick Mailbox Resynchronization", draft-ietf-lemonade-reconnect-client-03 (work in progress), February 2007. [IMAP-UIDPLUS] Crispin, M., "Internet Message Access Protocol (IMAP) - UIDPLUS extension", RFC 4315, December 2005. [IMAP-URLAUTH] Crispin, M., "Internet Message Access Protocol (IMAP) - URLAUTH Extension", RFC 4467, May 2006. [IMAP-WITHIN] Maes, S., "WITHIN Search extension to the IMAP Protocol", draft-ietf-lemonade-search-within-04 (work in progress), March 2007. [KEYWORDS] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [SMTP-8BITMIME] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. Crocker, "SMTP Service Extension for 8bit-MIMEtransport", RFC 1652, July 1994. Cridland, et al. Expires October 5, 2007 [Page 35] Internet-Draft Lemonade Profile April 2007 [SMTP-AUTH] Myers, J., "SMTP Service Extension for Authentication", RFC 2554, March 1999. [SMTP-BINARYMIME] Vaudreuil, G., "SMTP Service Extensions for Transmission of Large and Binary MIME Messages", RFC 3030, December 2000. [SMTP-BURL] Newman, C., "Message Submission BURL Extension", RFC 4468, May 2006. [SMTP-DSN] Moore, K., "Simple Mail Transfer Protocol (SMTP) Service Extension for Delivery Status Notifications (DSNs)", RFC 3461, January 2003. [SMTP-PIPELINING] Freed, N., "SMTP Service Extension for Command Pipelining", RFC 2197, September 1997. [SMTP-SIZE] Klensin, J., Freed, N., and K. Moore, "SMTP Service Extension for Message Size Declaration", STD 10, RFC 1870, November 1995. [SMTP-STATUSCODES] Freed, N., "SMTP Service Extension for Returning Enhanced Error Codes", RFC 2034, October 1996. [SMTP-TLS] Hoffman, P., "SMTP Service Extension for Secure SMTP over Transport Layer Security", RFC 3207, February 2002. [SUBMIT] Gellens, R. and J. Klensin, "Message Submission for Mail", RFC 4409, April 2006. [TLS-COMP] Hollenbeck, S., "Transport Layer Security Protocol Compression Methods", RFC 3749, May 2004. 14.2. Informative References [ESMTP] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [IMAP-SYNC-HOWTO] Cridland, et al. Expires October 5, 2007 [Page 36] Internet-Draft Lemonade Profile April 2007 Melnikov, A., "Synchronization Operations for Disconnected IMAP4 Clients", RFC 4549, June 2006. [LEMONADE-DEPLOYMENTS] Gellens, R., "Deployment Considerations for lemonade- compliant Mobile Email", draft-ietf-lemonade-deployments-06 (work in progress), March 2007. [MANAGESIEVE] Martin, T. and A. Melnikov, "A Protocol for Remotely Managing Sieve Scripts", draft-martin-managesieve-07 (work in progress), November 2006. [MEM-arch] Open Mobile Alliance, "Mobile Email Architecture Document", OMA (Work in Progress), http://www.openmobilealliance.org/, October 2005. [MEM-req] Open Mobile Alliance, "Mobile Email Requirements Document", OMA http://www.openmobilealliance.org/ release_program/docs/RD/ OMA-RD-MobileEmail-V1_0_20051018-C.pdf, Oct 2005. [SIEVE] Showalter, T. and P. Guenther, "Sieve: An Email Filtering Language", draft-ietf-sieve-3028bis-12 (work in progress), February 2007. Authors' Addresses Dave Cridland (editor) Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK Email: dave.cridland@isode.com Cridland, et al. Expires October 5, 2007 [Page 37] Internet-Draft Lemonade Profile April 2007 Alexey Melnikov (editor) Isode Limited 5 Castle Business Village 36 Station Road Hampton, Middlesex TW12 2BX UK Email: Alexey.Melnikov@isode.com Stephane H. Maes (editor) Oracle MS 4op634, 500 Oracle Parkway Redwood Shores, CA 94539 USA Phone: +1-203-300-7786 Email: stephane.maes@oracle.com Cridland, et al. Expires October 5, 2007 [Page 38] Internet-Draft Lemonade Profile April 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Cridland, et al. Expires October 5, 2007 [Page 39]