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Gordon L. Preston
X.400 and SMTP/MIME are the subject of much canonical debate in the messaging community. Although the general consensus is that X.400 offers better functionality than SMTP/MIME as an E-mail protocol, the decision to use X.400 or SMTP/MIME must be based not only on their functionality but also other issues such as security, systems management, message management, human resources requirements, and performance.
X.400 or SMTP/MIME? No matter what your choice in E-mail protocol, the pros and cons of each technology should be evaluated in the context of the real underlying issue keeping the network running.
Significant improvements in network management tools, utilities, and techniques are essential before a large, integrated network can begin cost-effective operations. The lack of adequate management tools at the application layer is a major impediment to implementing economical enterprisewide messaging systems. Operating such networks requires highly skilled software engineers who understand large-scale global enterprise networks.
This chapter covers the issues of operating a reliable messaging environment using either X.400 or SMTP as protocols to transfer E-mail. First, however, the basic features and philosophies of X.400 and SMTP/MIME are explained, including a brief look at the state of electronic mail (E-mail) today and the development process for each protocol.
Exploring critical networking issues requires an understanding of the basic features and philosophies of X.400 and SMTP/MIME, including a brief look at electronic mail (E-mail) today and the development process for each protocol.
X.400 is based on a formal messaging model created in standardization groups in the International Telecommunications UnionTelecommunications Standards Sector (ITU-TSS). It is the international standard for message handling. It is a full-feature, store-and-forward message-handling system designed to process multimedia and complex business documents.
In particular, X.400s specification of robust message delivery and non-delivery notification schemes makes it well suited to support electronic commerce transactions. X.400 is a commercially viable and secure message-handling technology supported by a worldwide infrastructure and officially sanctioned by various governments, telecommunication vendors, and public service providers. In addition, X.400 is designed to address not only messaging, but also directory, security, and network management.
Transmission Control Protocol/Internet Protocol (TCP/IP) is the de facto standard network protocol offering a connectionless-mode network service in the Internet suite of protocols. Simple mail transfer protocol (SMTP) is the application-level protocol offering message-handling service. However, because SMTP has its roots in the primarily academic and research and development background of the Internet Engineering Task Force (IETF), its use has been in a relatively benign and open environment without the need for rigidly enforced network performance, security, and message-delivery criteria.
Messaging by SMTP has been greatly enhanced with the development of Multipurpose Internet Mail Extensions (MIME). This is the official proposed standard format for multimedia Internet mail encapsulated inside standard Internet Request for Comment (RFC) 822 messages.
In simpler terms, MIME provides a way to exchange multimedia E-mail among many different computer systems. It is a collection of specifications that describe how mail user agents (MUAs) can identify arbitrary document types and message body types so the interface can decide how best to display the incoming data to the user. All the information about the attachment is embedded in the message itself. The MUA redefines the structure and contents of RFC 822 message bodies. Users can send word processor documents, spreadsheets, audio files, images, and textual data to someone else regardless of the platform, mail transport agent (MTA), or network operational system that is used by the sender or receiver.
E-mail is by far the most popular application carried over the Internet. Internet mail is based on various RFCs, including RFC 822 for SMTP.
E-mail with SMTP has become very popular in research, development, and engineering environments because of their use of UNIX. UNIX and engineering environments usually have TCP/IP and SMTP interconnection protocols bundled in with their operating systems. The Internet has proved to be eminently successful in providing information services to a widely diverse worldwide community with more than 9.4 million host computers on the Internet. One hundred and twenty nine countries now have direct connectivity to the Internet and 39 million users are reachable by E-mail. (A full report is available at http://www.nw.com/zone/WWW/report.html.)
X.400 was designed as a total international messaging environment from the beginning, whereas SMTP developed as an outgrowth of earlier experimental work on the Defense Advanced Researched Projects Agency (DARPA) Network. X.400 provides a complete set of internationally agreed-to standards; approved SMTP/MIME RFCs do not have the same level of official international agreement and approval. The unified design of X.400 as a total messaging environment is also reflected in its clean design interfaces with other international standards required to provide a messaging service namely, directory (X.500), management (X.700), and security (X.900) services.
SMTP is an outgrowth of the Internet and the Internet Engineering Task Force (IETF). As a quasi-official body with no set membership, the IETF is not necessarily representative of all potential customers needs. It has primary responsibility for the development and review of potential Internet standards from all sources. The IETFs working groups pursue specific technical issues, frequently resulting in the development of one or more specifications that are proposed for adoption as Internet standards. Most IETF members agree that the greatest benefit for all Internet community members results from the cooperative development of technically superior protocols and services.
SMTP/MIME, although capable of interfacing with these other international standards, does not work with the same level of designed interoperability as does X.400. This lack of designed interoperability will directly (and negatively) impact system operational maintenance and management costs.
There is no right or wrong answer when it comes to making a choice between X.400 and SMTP. The choice of technology depends on each organizations particular needs and which strength or weakness of different technologies is most important to them. An organization that wants to share similar technology with as many people as possible can effectively use SMTP/MIME. If security, increased functionality, and operational features such as guaranteed message traceability are most important, then X.400 is the answer.
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