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Exhibit 1. Strengths and Weaknesses of SMTP/MIME
Strengths Weaknesses

Very popular in the marketplace with millions of users worldwide Lacks functionality
Low cost Sendmail is free
Available on numerous platforms Implementations differ
Text body parts keep everything simple Too simple for some uses
Runs over IP, which comes with UNIX Limited security
Simple addressing Questionable for financial transactions
Simple message routing with DNS Uses DNS
Simplicity and flexibility of the format of RFC #822 messages Simplicity and flexibility of the format of RFC #822 messages
Numerous gateways available Lack of structure

SMTP/MIME CHARACTERISTICS

SMTP/MIME supports the transmission of sophisticated information, including images and video, yet it is simple in its design and extensible in nature because of its unique content-type/subtype body part identification mechanism. In short, SMTP/MIME provides a low-cost solution for messaging backbones.

Each part of a multimedia message identifies what type of information is carried in the message part. An entire MIME message, as opposed to an individual part of a multimedia message, can also have a type. For example, a message might have the type “text/plain” and consist of entirely plain text. A MIME message containing parts of different types has the umbrella type “multipart/mixed.” Many types and subtypes have been defined to include audio, image, external data source reference, and partial messages.

The simplicity and flexibility of SMTP/MIME are its main strengths because it can easily be implemented on all systems. Its weaknesses include no support for non-ASCII character sets, limited header structure, and an unstructured message body.

Exhibit 1 summarizes the strengths and weaknesses of SMTP/MIME.

X.400 CHARACTERISTICS

The ITU-TSS has developed an ambitious set of standards for electronic messaging called the X.400 message-handling system (MHS) and the X.500 directory services standards. X.400 has a very complete set of functional characteristics and can accommodate any type of messaging from simple interpersonal text to attached graphics, voice, and video clips. X.435 is defined for electronic commerce, using basic MHS components. X.400 is based on a functional model consisting of a few main components:

  User agents (UAs) Used on the desktop for message creation/reading.
  Message store (MS) Stores messages until recipient chooses to read them.
  Message transfer agents (MTAs) Stores and forwards messages within and between networks.
  Access units (AUs) Interfaces to other messaging entities (i.e., voice, facsimile, telex, physical delivery).

An X.500 directory is a collection of entries that contain information about things such as countries, organizations, people, computers, security, and application programs. The directory is a collection of one or more directory system agent (DSA) computers, each of which holds information for some portion of the directory.

Users access the X.500 directory via a computer process referred to as a directory user agent (DUA). Specific protocols have been developed to control directory access and the exchange of information with distributed directories.

X.500 is absolutely essential for implementing the address translation, document conversion, and sophisticated message routing needed for large-scale E-mail integration efforts. Directory synchronization is the basis for implementing transparent user addresses between systems.

X.400/X.500 systems are used by most of the world’s telecommunication service providers. The U.S. government is implementing a global X.400 messaging system for the military called the Defense Message System (DMS). NATO is also working toward implementing an X.400-based messaging system. This system defines a military message-handling system (MMHS) using X.400, similar to DMS. The militaries of Australia, Canada, the United Kingdom, and New Zealand are also implementing X.400-based MMHS. X.400 is the preferred technology for backbone messaging services of several large commercial companies in the U.S. and is widely used in Europe.

The strengths and weaknesses of X.400 are summarized in Exhibit 2.

INDUSTRIAL-STRENGTH MESSAGING REQUIREMENTS

X.400 has superior functionality defined in the standards, although many of these enhanced functions, such as multimedia and security, have yet to be deployed commercially. Electronic commerce using X.435 is still waiting for large industry segments to take advantage of this defined standard. Additionally, features such as delivery notifications, delivery to alternate recipients, and receipt notifications are critical to “industrial strength” messaging systems needed by large commercial organizations or a system such as DMS.

Exhibit 2. Strengths and Weaknesses of X.400
Strengths Weaknesses

Rigorous standards process through ITU Rigorous standards process through ITU
International standard for message handling Expensive
Functionality Complex to understand and configure
Robust message delivery and non-delivery schemes Not widely accepted by commercial marketplace
Well suited for electronic commerce Lack of robust user agents from popular vendors
Strong security standards defined Security implementations lagging
Works well with X.500 directory services X.500 complex to implement
Predictable performance Overhead is significant

SMTP, as defined by RFC 822, lacks the functionality required for backbone messaging systems or a highly complex network such as DMS. However, several improvements have taken place over the past few years. Functionality enhancements defined under MIME to extend SMTP and provide for messages with enclosed software objects such as images, video, audio, and binary file data have greatly enhanced Internet mail use for large organizations. Privacy Enhanced Mail (PEM) RFCs address many shortcomings with regard to security. These RFCs define data confidentiality, authenticity, integrity and nonrepudiation, message encipherment, and digital signatures.


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