Internet E-Mail Services

Mail is the most common service available on Internet. With capabilities far exceeding traditional mail services or telephone messaging systems, its importance has grown dramatically over the past decade. Its unhindered and continuous operation is critical to many organizations worldwide for exchange of information. This is to the extent that a one day interruption in service is viewed with grave concern and all efforts are made to restore service as soon as possible.

Over the years, use of Internet e-mail has grown especially rapidly in the academic and research community: colleges, universities, government and private research institutions and scientific centers. Topics discussed and information exchanged through this medium range from politics and history to critical experimental data and theoretical developments in the sciences and engineering. Often such dialogues are carried out through mailing lists -- that is, long-lasting distribution lists involving people who want to hold extended discussions on the same subjects. There are also computer conferencing systems available which allow large groups of people to post messages to all members of the group. Such systems provide for sophisticated user interfaces and separation of messages into categories by topic. They are used for detailed threads of discussions within continuous topics.

Table tab:InternetEmailServices presents an overview of the services available, and some general comments about them.

The common Envelope and Header fields, From, To, Cc, Bcc, Date, Subject, ...are all supported. These fields identify the sender of the message, the receiver(s), message date and the subject (as specified by the sender) of the message. Non-Delivery Reports are supported. Delivery reports and Notifications of receipt of e-mail are not supported.

Delivery can be to a number of users at the same time, as specified in a distribution list. Forwarding of mail to other address(es) is also supported.

Security issues such as privacy and authentication are included as enhancements to the basic service through Privacy Enhanced E-Mail (PEM). Incorporation of complex body parts is through the Multipurpose Internet Mail Extensions (MIME).

Frequently the issues of "size" and "message routing" are of interest to users of Internet e-mail. As with many evolutionary realities, support for "size" is not uniform throughout the whole network. However facilities that provide for segmentation and re-assembly do exist. At a minimum, message sizes up to 64 K bytes can be reliably routed, though in many cases this figure is 1 M Byte or more.

Routing of messages in a network of 4.8 million hosts is non-trivial. A great deal of the success of Internet E-Mail can be attributed to Domain Name System (DNS). DNS is a directory service that maps host names to host addresses and also accommodates routing of e-mail.