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This document specifies the architecture for mobile email, as described by the OMA, using Internet Mail protocols. This architecture is the basis of the work of the LEMONADE WG and is a guideline for the LEMONADE Profile.
1.
Introduction
2.
OMA Mobile Email (MEM)
2.1.
OMA MEM Requirements
2.2.
OMA MEM Architecture
2.2.1.
OMA MEM logical Architecture
2.2.2.
OMA MEM Deployment Issues
2.3.
OMA MEM Technical Specification
3.
IETF LEMONADE Architecture
3.1.
Relationship between the OMA MEM and LEMONADE logical architectures
3.2.
LEMONADE realization of OMA MEM with non-LEMONADE compliant servers
3.2.1.
LEMONADE realization of OMA MEM with non-LEMONADE IMAP servers
3.2.2.
LEMONADE realization of OMA MEM with non-IMAP servers
4.
Filters and server to client notifications and LEMONADE
5.
Security Considerations
6.
IANA considerations
7.
Acknowledgements
8.
Informative References
§
Authors' Addresses
§
Intellectual Property and Copyright Statements
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This document describes the architecture of OMA mobile email (MEM) using Internet Mail protocols defined by the IETF. The LEMONADE work group has enhanced many of these protocols for use in the mobile environment and are summarized in the LEMONADE profile (Maes, S. and A. Melnikov, “Internet Email to Support Diverse Service Environments (Lemonade) Profile,” June 2006.) [PROFILE] and its revision LEMONADE profile bis (Cridland, D., Melnikov, A., and S. Maes, “The Lemonade Profile,” June 2008.) [PROFILE‑bis]. This document shows how the OMA MEM Requirement document (Open Mobile Alliance, “Mobile Email Requirements Document,” Oct 2005.) [MEM‑req], OMA MEM Architecture (Open Mobile Alliance, “Mobile Email Architecture Document,” June 2007.) [MEM‑arch], and OMA MEM Technical Specification (Open Mobile Alliance, “Mobile Email Technical Specification,” Oct 2007.) [MEM‑ts] relate to the work of LEMONADE.
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The OMA Mobile Email (MEM) sub-working group has spent some time studying the requirements and architecture of mobile email. IETF LEMONADE has been liaising with them and has based much of our Internet Mail enhancements based on their input. This section summarizes the output of the OMA.
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The OMA MEM activity collected a set of use cases and derived requirements for a mobile email enabler (MEM). The OMA MEM Requirements (Open Mobile Alliance, “Mobile Email Requirements Document,” Oct 2005.) [MEM‑req] summarizes this work. Some requirements relates 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.
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This section introduces the OMA MEM Architecture.
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The OMA MEM activity has derived a logical architecture from the requirements and use cases described in [MEM‑req] (Open Mobile Alliance, “Mobile Email Requirements Document,” Oct 2005.). A simplification for illustrative purposes is shown in Figure 1 (Basic OMA MEM logical architecture), where arrows indicate content flows.
__________
| Other |
+---| Mobile |<--+
| | Enablers | |
| |__________| |
|ME-4 |ME-3
_v____ ___v____ ________
| |ME-1 | | | |
| MEM |-------->| MEM | I2 | Email |
|Client| ME-2| Server |<---->| Server |
|______|<--------|________| |________|
^
|ME-5
|
| Figure 1: Basic OMA MEM logical architecture |
Figure 1 (Basic OMA MEM logical architecture) identifies the following elements:
OMA identifies different interfaces:
The MEM server enables an email server. In a particular implementation, the email server may be packaged with (internal to it) the MEM server or be a separate component. In such cases, interfaces to the email server are out of scope of the OMA MEM specifications. In the present document, we focus on the case where the backend consists of IETF IMAP and Submit servers. However, we also discuss the relationship to other cases. The I2 interface is an OMA notation to designate protocol / interfaces that are not specified by the MEM enabler but may be standardized elsewhere.
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The OMA MEM Architecture document (Open Mobile Alliance, “Mobile Email Architecture Document,” June 2007.) [MEM‑arch] further identifies deployment models.
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The OMA MEM Architecture document (Open Mobile Alliance, “Mobile Email Architecture Document,” June 2007.) [MEM‑arch] identifies OMA MEM server proxies as server components that may be deployed ahead of firewalls to facilitate firewall traversal.
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OMA MEM identifies that each component (MEM client, MEM servers, other enablers, and the email server) may be deployed in different domains, possibly separated by firewalls and other network intermediaries. MEM proxies may be involved in front of firewall that protects the MEM server domain.
OMA MEM targets support of configurations where:
The e-mail service provider can be either a third-party service provider, a network service provider, or an enterprise e-mail service.
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The OMA MEM activity will conclude with a specification for a mobile email enabler (MEM). The ongoing work is in OMA MEM Technical Specification (Open Mobile Alliance, “Mobile Email Technical Specification,” Oct 2007.) [MEM‑ts]. LEMONADE is a basis for the mechanism. However, some additional details that are outside the scope of IETF will also be included.
OMA provides ways to perform provisioning via OMA client provisioning and device management. Other provisioning specifications are available (e.g., SMS based).
OMA provides enablers to support out-of-band notification mechanisms, as well as filter specifications (such as XDM), remote device deactivation, and other, non-Internet activities.
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This section introduces the LEMONADE Architecture.
The IETF LEMONADE activity has derived a LEMONADE profile (Cridland, D., Melnikov, A., and S. Maes, “The Lemonade Profile,” June 2008.) [PROFILE‑bis] with the logical architecture represented in Figure 2 (LEMONADE logical architecture), 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 2: LEMONADE logical architecture |
The LEMONADE profile (Maes, S. and A. Melnikov, “Internet Email to Support Diverse Service Environments (Lemonade) Profile,” June 2006.) [PROFILE] assumes:
Further details on the IETF email protocol stack and architecture can be found in [MAIL] (Crocker, D., “Internet Mail Architecture,” February 2008.)
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Figure 3 (Mapping of LEMONADE logical architecture onto the OMA MEM logical architecture) illustrates the mapping of the IETF LEMONADE logical architecture on the OMA MEM logical architecture.
_____________________
| 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 3: Mapping of LEMONADE logical architecture onto the OMA MEM logical architecture |
As described in Section 3 (IETF LEMONADE Architecture), 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 servers. Mapping to the OMA MEM logical architecture, for the case considered and specified by the LEMONADE profile, we logically combine the MEM server and email server. However, in lemonade we split them logically into a distinct LEMONADE message store and a LEMONADE submit server. ME-2 consists of two interfaces. ME-2a is IMAP extended according to the LEMONADE profile. ME-2b is SUBMIT extended according to the LEMONADE profile.
The MUA is part of the MEM client.
The external notifications mechanism is part of OMA enablers specified by the OMA.
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The OMA MEM activity is not limited to enabling Lemonade compliant servers. It explicitly identifies the need to support other back-ends. This is, of course, outside the scope of the IETF Lemonade activity.
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Figure 4 (Architecture to support non-LEMONADE IMAP servers with a LEMONADE realization of an OMA MEM enabler) illustrates the case of IMAP servers that are not LEMONADE compliant. In such case, the I2 interface between the MEM server components and the IMAP store and submit server are IMAP and SUBMIT without Lemonade extensions.
______________
| |
_________| 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 4: Architecture to support non-LEMONADE IMAP servers with a LEMONADE realization of an OMA MEM enabler |
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Figure 5 (Architecture to support non-IMAP servers with a LEMONADE realization of OMA MEM enabler.) 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 5: Architecture to support non-IMAP servers with a LEMONADE realization of OMA MEM enabler. |
I2 designates proprietary adapters to the back-ends.
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OMA MEM RD (Open Mobile Alliance, “Mobile Email Requirements Document,” Oct 2005.) [MEM‑req] and AD (Open Mobile Alliance, “Mobile Email Architecture Document,” June 2007.) [MEM‑arch] emphasize the need to provide mechanisms for server to client notifications of email events and filtering. Figure 6 (Filtering mechanism defined in LEMONADE architecture) illustrates how notification and filtering works in the LEMONADE profile (Maes, S. and A. Melnikov, “Internet Email to Support Diverse Service Environments (Lemonade) Profile,” June 2006.) [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 6: Filtering mechanism defined in LEMONADE architecture |
In Figure 6 (Filtering mechanism defined in LEMONADE architecture), we define four categories of filters:
The MUA can manage the NF and DF filters using the SIEVE management protocol (Melnikov, A. and T. Martin, “A Protocol for Remotely Managing Sieve Scripts,” June 2008.) [MANAGESIEVE].
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We note there are security risks associated with:
We refer the reader to the relevant Internet Mail, IMAP, SUBMIT, and Lemonade documents for how we address these issues.
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None.
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The authors acknowledge and appreciate the work and comments of the IETF LEMONADE working group and the OMA MEM working group. We extracted the contents of this document from sections of draft-ietf-lemonade-profile-bis-05.txt by Stephane Maes, Alexey Melnikov and Dave Cridland, as well as sections of draft-ietf-lemonade-notifications-04.txt by Stephane Maes and Ray Cromwell.
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| [MEM-arch] | Open Mobile Alliance, “Mobile Email Architecture Document,” June 2007. |
| [MEM-req] | Open Mobile Alliance, “Mobile Email Requirements Document,” OMA http://www.openmobilealliance.org/, Oct 2005. |
| [MEM-ts] | Open Mobile Alliance, “Mobile Email Technical Specification,” OMA (Work in Progress), http://www.openmobilealliance.org/, Oct 2007. |
| [PROFILE] | Maes, S. and A. Melnikov, “Internet Email to Support Diverse Service Environments (Lemonade) Profile,” RFC 4550, June 2006 (TXT). |
| [PROFILE-bis] | Cridland, D., Melnikov, A., and S. Maes, “The Lemonade Profile,” draft-ietf-lemonade-profile-bis-09 (work in progress), June 2008 (TXT). |
| [RFC3501] | Crispin, M., “INTERNET MESSAGE ACCESS PROTOCOL - VERSION 4rev1,” RFC 3501, March 2003 (TXT). |
| [RFC2821] | Klensin, J., “Simple Mail Transfer Protocol,” RFC 2821, April 2001 (TXT). |
| [RFC4409] | Gellens, R. and J. Klensin, “Message Submission for Mail,” RFC 4409, April 2006 (TXT). |
| [RFC5230] | Showalter, T. and N. Freed, “Sieve Email Filtering: Vacation Extension,” RFC 5230, January 2008 (TXT). |
| [SIEVE] | Guenther, P. and T. Showalter, “Seive: An Email Filtering Language,” RFC 5528, January 2008. |
| [NOTIFICATIONS] | Gellens, R. and S. Maes, “Lemonade Notifications Architecture,” draft-ietf-lemonade-notifications-10 (work in progress), July 2008 (TXT). |
| [MAIL] | Crocker, D., “Internet Mail Architecture,” draft-crocker-email-arch-10 (work in progress), February 2008 (TXT). |
| [MANAGESIEVE] | Melnikov, A. and T. Martin, “A Protocol for Remotely Managing Sieve Scripts,” draft-martin-managesieve-10 (work in progress), June 2008 (TXT). |
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| Eric W. Burger | |
| New Hampshire | |
| USA | |
| Phone: | |
| Fax: | +1 530-267-7447 |
| Email: | eburger@standardstrack.com |
| URI: | http://www.standardstrack.com |
| Glenn Parsons | |
| Nortel Networks | |
| 3500 Carling Avenue | |
| Ottawa, ON K2H 8E9 | |
| Canada | |
| Phone: | +1 613 763 7582 |
| Email: | gparsons@nortel.com |
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