X.400
Encyclopedia
X.400 is a suite of ITU-T
Recommendations that define standards for Data Communication Networks for Message Handling Systems (MHS) — more commonly known as "email
".
At one time X.400 was expected to be the predominant form of email, but this has role has been taken by the SMTP-based Internet
e-mail. Despite this, it has been widely used within organizations, was a core part of Microsoft Exchange Server
until 2006, and variants continue to be important in military and aviation contexts.
Developed in cooperation with the ISO
, the X.400-series recommendations specify OSI
standard protocols for exchanging and addressing electronic messages. The companion F.400-series of recommendations define Message Handling Services built on Message Handling Systems (MHS), as well as access to and from the MHS for public services. In the late 1990s the ITU-T
consolidated recommendations F.400 and X.400 and published the ITU-T
F.400/X.400 (06/1999) recommendation "Message handling system and service overview".
The X.400-series recommendations define the technical aspects of the MHS: ITU-T
Rec. X.402 | (ISO
/IEC
10021-2) defines the overall system architecture of an MHS, ITU-T
Rec. X.411 | (ISO
/IEC
10021-4) defines the Message Transfer Service (MTS) and its functional component the Message Transfer Agent (MTA)
, and ITU-T
Rec. X.413 | (ISO
/IEC
10021-5) defines the Message Store. All ITU-T
recommendations provide specific terms for descriptions of system entities and procedures. For example, messages (email) exchanged among people is referred to as Interpersonal Messaging (IPM); electronically structured business documents (e.g., invoices, purchase orders, dispatch advice, etc.) exchanged among trading partners’ computers fall under the EDI
protocols.
As with most ISO
standards dealing with application-level
networking, X.400 failed to compete successfully with SMTP, the Internet-based equivalent in North America. However, in Europe, South America, and Asia, X.400 is quite widely implemented, especially for EDI services. In North America X.400 is still used in some applications, such as the military, intelligence services and aviation, mainly because the X.400 functions for integrity and security were developed and deployed much earlier than their SMTP counterparts (S/MIME
, PGP
and SMTP-TLS). For similar reasons it is sometimes used for transmission of EDI messages between applications.
Message handling is a distributed information processing task that integrates two related subtasks: message transfer and message storage. The ITU-T
Recommendations define specific protocols for a wide-range of communication tasks. For example, the P1 protocol is used explicitly for communication among MTA
s, P3 between the user agent
and an MTA, and P7 between the user agent and message store.
In the 1994 version P7 was enhanced to provide folders in the message store, allow storage of submitted messages, and provide many automatic actions such as auto-foldering and correlation of replies, delivery reports and receipt notifications with submitted messages.
X.400 message content standards are defined for communication between user agents. These are modelled as conceptual protocols that treat P1 and P3/P7 as providing an underlying reliable transport of message contents. The message content standard for interpersonal messaging, IPM, defined in ITU-T Rec. X.420 | ISO/IEC 10021-7 was named P2 in the Red Book. The extended version of IPM in the Blue Book was given content-type 22 (for P2 version 2) and is often referred to informally as P22, although that term is not used in the standards. The message content standard for EDI
is defined in ITU-T Rec. F.435 | ISO/IEC 10021-8 and ITU-T Rec. X.435 | ISO/IEC 10021-9, and informally referred to as P35. A voice messaging content type is defined in ITU-T Recs. F.440 and X.440.
Important features of X.400 include structured addressing, ASN.1 binary code enabling multimedia content (predating and more efficient than MIME
), and integrated security capabilities. As X.400 inter-domain relay services were assumed by ITU to be run by PTT
s, X.400 incorporated fields for the automated transfer of messages between X.400 and other PTT services, such as Telex
, facsimile
and physical postal mail. ISO later added open routing standards (ITU-T Rec. X.412 | ISO/IEC 10021-10 and ITU-T Rec. X.404 | ISO/IEC 10021-11), but the initial misconception that X.400 required PTT relay services, coupled with PTT volume-based charges for these, were factors that inhibited the widespread uptake of X.400.
X.400 has been extended for use in military applications (see MMHS) and aviation (see AMHS
).
The standards themselves originally did not specify how these email addresses should be written (for instance on a business card); RFC 1685 specified one encoding, based on a 1993 draft of ITU-T Recommendation F.401 which looked like "G=Harald;S=Alvestrand;O=Uninett;P=Uninett;A=;C=no" — the unwieldiness of this addressing format is believed by many to be one factor in the lack of success of X.400.
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Recommendations that define standards for Data Communication Networks for Message Handling Systems (MHS) — more commonly known as "email
Email
Electronic mail, commonly known as email or e-mail, is a method of exchanging digital messages from an author to one or more recipients. Modern email operates across the Internet or other computer networks. Some early email systems required that the author and the recipient both be online at the...
".
At one time X.400 was expected to be the predominant form of email, but this has role has been taken by the SMTP-based Internet
Internet
The Internet is a global system of interconnected computer networks that use the standard Internet protocol suite to serve billions of users worldwide...
e-mail. Despite this, it has been widely used within organizations, was a core part of Microsoft Exchange Server
Microsoft Exchange Server
Microsoft Exchange Server is the server side of a client–server, collaborative application product developed by Microsoft. It is part of the Microsoft Servers line of server products and is used by enterprises using Microsoft infrastructure products...
until 2006, and variants continue to be important in military and aviation contexts.
History
The first X.400 Recommendations were published in 1984 (Red Book), and a substantially revised version was published in 1988 (Blue Book). New features were added in 1992 (White Book) and subsequent updates. Although X.400 was originally designed to run over the OSI Transport service, an adaptation to allow operation over TCP/IP, RFC 1006, has become the most popular way to run X.400.Developed in cooperation with the ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
, the X.400-series recommendations specify OSI
Open Systems Interconnection
Open Systems Interconnection is an effort to standardize networking that was started in 1977 by the International Organization for Standardization , along with the ITU-T.-History:...
standard protocols for exchanging and addressing electronic messages. The companion F.400-series of recommendations define Message Handling Services built on Message Handling Systems (MHS), as well as access to and from the MHS for public services. In the late 1990s the ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
consolidated recommendations F.400 and X.400 and published the ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
F.400/X.400 (06/1999) recommendation "Message handling system and service overview".
The X.400-series recommendations define the technical aspects of the MHS: ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Rec. X.402 | (ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
10021-2) defines the overall system architecture of an MHS, ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Rec. X.411 | (ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
10021-4) defines the Message Transfer Service (MTS) and its functional component the Message Transfer Agent (MTA)
Mail transfer agent
Within Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...
, and ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Rec. X.413 | (ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
/IEC
International Electrotechnical Commission
The International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
10021-5) defines the Message Store. All ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
recommendations provide specific terms for descriptions of system entities and procedures. For example, messages (email) exchanged among people is referred to as Interpersonal Messaging (IPM); electronically structured business documents (e.g., invoices, purchase orders, dispatch advice, etc.) exchanged among trading partners’ computers fall under the EDI
Electronic Data Interchange
Electronic data interchange is the structured transmission of data between organizations by electronic means. It is used to transfer electronic documents or business data from one computer system to another computer system, i.e...
protocols.
As with most ISO
International Organization for Standardization
The International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
standards dealing with application-level
Application layer
The Internet protocol suite and the Open Systems Interconnection model of computer networking each specify a group of protocols and methods identified by the name application layer....
networking, X.400 failed to compete successfully with SMTP, the Internet-based equivalent in North America. However, in Europe, South America, and Asia, X.400 is quite widely implemented, especially for EDI services. In North America X.400 is still used in some applications, such as the military, intelligence services and aviation, mainly because the X.400 functions for integrity and security were developed and deployed much earlier than their SMTP counterparts (S/MIME
S/MIME
S/MIME is a standard for public key encryption and signing of MIME data. S/MIME is on an IETF standards track and defined in a number of documents, most importantly RFCs. S/MIME was originally developed by RSA Data Security Inc...
, PGP
Pretty Good Privacy
Pretty Good Privacy is a data encryption and decryption computer program that provides cryptographic privacy and authentication for data communication. PGP is often used for signing, encrypting and decrypting texts, E-mails, files, directories and whole disk partitions to increase the security...
and SMTP-TLS). For similar reasons it is sometimes used for transmission of EDI messages between applications.
Message handling is a distributed information processing task that integrates two related subtasks: message transfer and message storage. The ITU-T
ITU-T
The ITU Telecommunication Standardization Sector is one of the three sectors of the International Telecommunication Union ; it coordinates standards for telecommunications....
Recommendations define specific protocols for a wide-range of communication tasks. For example, the P1 protocol is used explicitly for communication among MTA
Mail transfer agent
Within Internet message handling services , a message transfer agent or mail transfer agent or mail relay is software that transfers electronic mail messages from one computer to another using a client–server application architecture...
s, P3 between the user agent
E-mail client
An email client, email reader, or more formally mail user agent , is a computer program used to manage a user's email.The term can refer to any system capable of accessing the user's email mailbox, regardless of it being a mail user agent, a relaying server, or a human typing on a terminal...
and an MTA, and P7 between the user agent and message store.
In the 1994 version P7 was enhanced to provide folders in the message store, allow storage of submitted messages, and provide many automatic actions such as auto-foldering and correlation of replies, delivery reports and receipt notifications with submitted messages.
X.400 message content standards are defined for communication between user agents. These are modelled as conceptual protocols that treat P1 and P3/P7 as providing an underlying reliable transport of message contents. The message content standard for interpersonal messaging, IPM, defined in ITU-T Rec. X.420 | ISO/IEC 10021-7 was named P2 in the Red Book. The extended version of IPM in the Blue Book was given content-type 22 (for P2 version 2) and is often referred to informally as P22, although that term is not used in the standards. The message content standard for EDI
EDI
EDI may refer to:* Efficient Drivetrains Inc.* Electronic Data Interchange, a particular set of standards for computer-to-computer exchange of information* EDI, Extended Destination Index...
is defined in ITU-T Rec. F.435 | ISO/IEC 10021-8 and ITU-T Rec. X.435 | ISO/IEC 10021-9, and informally referred to as P35. A voice messaging content type is defined in ITU-T Recs. F.440 and X.440.
Important features of X.400 include structured addressing, ASN.1 binary code enabling multimedia content (predating and more efficient than MIME
MIME
Multipurpose Internet Mail Extensions is an Internet standard that extends the format of email to support:* Text in character sets other than ASCII* Non-text attachments* Message bodies with multiple parts...
), and integrated security capabilities. As X.400 inter-domain relay services were assumed by ITU to be run by PTT
Postal Telegraph and Telephone
A postal, telegraph, and telephone service is a government agency responsible for postal mail, telegraph, and telephone services. Such monopolies existed in many countries, though not in North America or Japan. Many PTTs have been partially or completely privatized in recent years...
s, X.400 incorporated fields for the automated transfer of messages between X.400 and other PTT services, such as Telex
Teleprinter
A teleprinter is a electromechanical typewriter that can be used to communicate typed messages from point to point and point to multipoint over a variety of communication channels that range from a simple electrical connection, such as a pair of wires, to the use of radio and microwave as the...
, facsimile
Fax
Fax , sometimes called telecopying, is the telephonic transmission of scanned printed material , normally to a telephone number connected to a printer or other output device...
and physical postal mail. ISO later added open routing standards (ITU-T Rec. X.412 | ISO/IEC 10021-10 and ITU-T Rec. X.404 | ISO/IEC 10021-11), but the initial misconception that X.400 required PTT relay services, coupled with PTT volume-based charges for these, were factors that inhibited the widespread uptake of X.400.
X.400 has been extended for use in military applications (see MMHS) and aviation (see AMHS
Aeronautical Message Handling System
ATS Message Handling System also known as Aeronautical Message Handling System is a standard for aeronautical ground-ground communications based on X.400 profiles...
).
Addressing
An X.400 address consists of several elements, including:- C (Country name)
- ADMD (Administration Management Domain), usually a public mail service provider
- PRMD (Private Management Domain)
- O (Organization name)
- OU (Organizational Unit Names)
- G (Given name)
- I (Initials)
- S (Surname)
The standards themselves originally did not specify how these email addresses should be written (for instance on a business card); RFC 1685 specified one encoding, based on a 1993 draft of ITU-T Recommendation F.401 which looked like "G=Harald;S=Alvestrand;O=Uninett;P=Uninett;A=;C=no" — the unwieldiness of this addressing format is believed by many to be one factor in the lack of success of X.400.
External links
- International Telecommunication Union - Telecommunication Std. Sector - List of ITU-T Recommendations
- International Electrotechnical Commission - About the IEC
- Sending Messages - Routing and Transport - See "The Battle Between SMTP and X.400"
- Harald T. Alvestrand's X.400 FAQ - A comprehensive list of resources on x.400 series of standards (last updated in 1995)
- X400.org
X.400 Standards
X.400 standards are available free from ITU-T- ITU-T Rec. F.400/X.400 |ISO/IEC 10021-1 Message handling system and service overview
- ITU-T Rec. X.402 |ISO/IEC 10021-2 Message Handling Systems (MHS): Overall architecture
- ITU-T Rec. X.411 |ISO/IEC 10021-4 Message Handling Systems (MHS): Message Transfer System: Abstract Service Definition and Procedures
- ITU-T Rec. X.413 |ISO/IEC 10021-5 Message Handling Systems (MHS): Message store - Abstract service definition
- ITU-T Rec. X.419 |ISO/IEC 10021-6 Message Handling Systems (MHS): Protocol specifications
- ITU-T Rec. X.420 |ISO/IEC 10021-7 Message Handling Systems (MHS): Interpersonal Messaging System
- ITU-T Rec. X.435 |ISO/IEC 10021-9 Message Handling Systems (MHS): Electronic data interchange messaging system
- ITU-T Rec. X.412 |ISO/IEC 10021-10 Message Handling Systems (MHS): MHS routing
- ITU-T Rec. X.404 |ISO/IEC 10021-11 Message Handling Systems (MHS): MHS routing - Guide for messaging systems managers
X.400 Products
- Logsys - ISOPLEX X.400: Vendor and Developer.
- Compucat Research - Compucat Message eXchange (CMX)
- AddOnMail - Editor of X.400 user agent software
- Boldon James - Vendor of X.400 user agent software
- Deep-Secure - High assurance boundary protection guards, and Military Messaging clients and servers
- Galadrium - LUNAR X.400 User Agent
- Isode Ltd - M-Switch X.400 & M-Store X.400
- NET-TEL - X.400 clients (user agents) and servers (MTA and P7 MS)
- Atos Origin - MXMS X.400 server
- Xelas Software - Vendor X.400 Message Handling System
- Microsoft Exchange ServerMicrosoft Exchange ServerMicrosoft Exchange Server is the server side of a client–server, collaborative application product developed by Microsoft. It is part of the Microsoft Servers line of server products and is used by enterprises using Microsoft infrastructure products...
- the core engine of versions 4.0 (the original release) through 5.x were based on an implementation of the X.400 standard. The next version, Exchange 2000, replaced this with an SMTP-based engine. (note, however, that all versions support MTAs to permit connectivity to SMTP, X.400, and other mail systems)
See also
- StandardizationStandardizationStandardization is the process of developing and implementing technical standards.The goals of standardization can be to help with independence of single suppliers , compatibility, interoperability, safety, repeatability, or quality....
- Standards organizationStandards organizationA standards organization, standards body, standards developing organization , or standards setting organization is any organization whose primary activities are developing, coordinating, promulgating, revising, amending, reissuing, interpreting, or otherwise producing technical standards that are...
- International Telecommunication UnionInternational Telecommunication UnionThe International Telecommunication Union is the specialized agency of the United Nations which is responsible for information and communication technologies...
(ITU) - International Electrotechnical CommissionInternational Electrotechnical CommissionThe International Electrotechnical Commission is a non-profit, non-governmental international standards organization that prepares and publishes International Standards for all electrical, electronic and related technologies – collectively known as "electrotechnology"...
(IEC) - International Organization for StandardizationInternational Organization for StandardizationThe International Organization for Standardization , widely known as ISO, is an international standard-setting body composed of representatives from various national standards organizations. Founded on February 23, 1947, the organization promulgates worldwide proprietary, industrial and commercial...
(ISO) - Electronic Data InterchangeElectronic Data InterchangeElectronic data interchange is the structured transmission of data between organizations by electronic means. It is used to transfer electronic documents or business data from one computer system to another computer system, i.e...
(ANSI Standard) - Message Handling System (unrelated Novell email protocol)