Contents:

• About Electronic Mail
• How U.S. Mail Works
• How Electronic Mail Works
• About Internet Addressing
• The Expanded Address
• Some Commonly Used Networks
• National Networks
• Finding an E-Mail Address
• Come Commonly Used Gateways
• Other Questions

About Electronic Mail

Electronic mail (or "e-mail") is a service by which people with accounts on one computer can send messages to people with accounts on other computers, whether they are at Rutgers, across the country, or around the world. Such messages are sent over the Internet network, which is a system of computers linked by cables and telephone lines.

How U. S. Mail Works

For comparison's sake:

1. You write a letter.
2. You address it, put it in an envelope, and stamp it.
3. You drop it in a mailbox.
4. A mail carrier takes it to the post office.
5. It's sorted along with other letters for similar addresses.
6. Letters for one region are taken to that region.
7. At a regional post office, the letters are separated into local addresses.
8. The local mail carrier delivers your letter.

Figure 1

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How Electronic Mail Works

The steps followed in composing and delivering an e-mail message are directly analogous to those followed for the U. S. Mail system.

1. You write a letter with an editor.
2. You put it in a mail program, with an address in the form of:
• user@host.domain where
• user is a username or account on a computer;
• host is the computer name, sometimes also called a "node";
• domain is the network the computer is on.
3. You send it via the mail program.
4. The mail program puts additional information (called "headers''; see Figure 2) around the message and gives it to a "postmaster'' program.
5. The postmaster program determines how to reach the address.
6. A file transfer program sends it to a computer on the path (either the direct recipient or an intermediary).
7. If intermediaries are involved, they will repeat the previous step, as necessary, . . .
8. . . . until it reaches the host in your address, where the local postmaster program sends it to the appropriate user.
   

Figure 2: A Sample Internet Message

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About Internet Addressing

While other addressing schemes are in use around the world (host::user or host!user), the user@host.domain form is the one most commonly used. Because this form originated on the Internet network, it is called Internet-style addressing.

Figure 3: Sample Network

The Expanded Address

See Figure 3 for a sample network. Assume you are userA@host1. The following are valid addresses.

• userBfor a user on the same machine as you
• userC@host2for a user on a different machine in the same domain as you.
• userC@host2.domain1 also for a user on a different machine in the same domain as you. The explicit naming of the domain is not necessary in local domains (such as the RUNet). It is necessary when leaving the local domain for a larger one (such as the Internet).
• userD@host3.domain2for a user on a machine in another domain. For example, to send a message from the Internet to a user on the BITnet (see "Some Commonly Used Networks" below), the address would be user@host.BITNET
• userD@host3.site.domain2Some installations with many computers (such as Rutgers) have domains broken up into site and network. This also helps distinguish between computers with the same name on the same network.
• userD@host3.department.site.domain2Some installations break the site down further
• userD%host3.domain2@host2.domain1To a user on a machine that your machine can't reach but that an intermediate machine can. The intermediate machine is called a "gateway'', because it exists on 2 or more different networks and passes messages between them. The message is first sent to host2, where everything after the "@'' is stripped off. The "%'' is changed to an "@'', and host2 then mails the message to userD@host3.
  

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Some Commonly Used Networks

JANET is an international network of networks. All computers on the Internet use the Internet TCP/IP communications protocol (a particular method of passing messages between computers). Participating organizations include academic sites (such as Rutgers), government agencies, and businesses.

Though funded primarily by organizations in North America, the Internet is the closest thing to a global network, with participating sites all around the world and connections to many national networks, such as JANET, and other international networks, such as BITnet, UUCP, and Usenet. The "Internet'' is often used as a sloppy synonym for a true (though technically non-existant) global network. Participating networks include:

DDN, the Defense Data Network, which is itself a combination of MILNET, a secure network of U.S. military sites, both in North America and abroad, and other, smaller networks used by the U.S. military. (MILNET has replaced ARPANET, the predecessor of the Internet.)

NSFNET, the National Science Foundation NETwork, which includes supercomputer centers and other scientific and research sites funded by the NSF. CSNET, a network established to encourage cooperation between sites doing development work in computer science.

An Internet address can most easily be recognized by the final component of its domain:

com is the domain for commercial sites on the Internet.
edu is the domain for educational institutions on the Internet.
mil is the domain for military sites on the Internet.
gov is the domain for governmental organizations on the Internet.
org is the domain for various other organizations on the Internet.
net is the domain for Internet administrator sites.

For example, rci.rutgers.edu is an Internet address. Internet sites may also end in a two-character country abbreviation, as described below under "JANET''.

In 1991, the U.S. Congress authorized the creation of a true national network for the United States, NREN, the National Research and Education Network. This "information superhighway" may, someday, replace many of the networks currently comprising the Internet in the United States.

UUCP ("UNIX-to-UNIX Copy Program") and Usenet ("USEr's NETwork") are cooperative. UUCP and Usenet networks were originally developed for computers running the UNIX operating system. Now they include computers with a variety of operating systems, at a variety of commercial, academic, and governmental sites.

UUCP and Usenet support one type of electronic communication each: electronic mail for UUCP and Netnews for Usenet. UUCP's electronic mail is delivered directly from the originating site to the recipient via telephone lines.

Netnews is a distributed bulletin board or conferencing system. Instead of sending a message to one person, or to a mailing list for redistribution to a limited number of people, users send messages to a local database which anyone on that host can read. The contents of this database are also sent to neighboring sites, which send their messages back in return. In addition, messages received from still other sites are similarly passed around, until every site on the Usenet has a copy of every message.

While Netnews access is beyond the scope of this document, it is mentioned here because there is a very close, but not complete, overlap between sites running UUCP and sites running Usenet. Because of this, the two are often (though technically incorrectly) referred to together as Usenet. Rutgers is a main site, or "backbone", on the Usenet.

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National Networks

JANET is the network of computers in the United Kingdom. It is one of many national networks to be found in the world. Many of the national networks use Internet-style addressing with a domain component indicating the country of origin. For example:

.UK is the United Kingdom
.US is the United States
.DE is Germany ("DEutschland'')
.AU is AUstralia
.IL is IsraeL
.JP is JaPan

Internet sites put this component at the end of the domain: VM1.TAU.AC.IL However, JANET, while using an Internet-like domain component scheme, reverses the order, starting with the host on the right and ending with the country of origin on the left: UK.AC.UCL.CS.NSS. If you reply to a message received from the U.K., software at the gateways will automatically reorder the domains. However, if you are originating a message to the U.K., or if a correspondent has given you an address there, you must remember to reverse the order yourself, putting the host on the left and the .UK on the right, before sending a message.

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Finding an E-Mail Address

E-mail users often ask how to learn if a friend or colleague has an e-mail account. Unfortunately, there is nothing equivalent to the telephone directory, no file that lists all known e-mail accounts across the Internet.

The surest way to learn a person's e-mail address is to ask that person. This may require using a tool other than e-mail, such as the telephone, surface mail, or a meeting in person.

If you know that a person has an account on a particular computer, you can try the command finger user@host on our UNIX systems. Last names are the most common form of computer usernames. If the last name is common, you may need to preface the last name with the person's first (or first and middle) initial. However, there are some usernames that bear no relation to the person's actual name, so using finger becomes largely a matter of guesswork.

If you are looking for a person at Rutgers, you can try the wpwhois command on our UNIX systems (or use the Rutgers University Online Directory available on the Rutgers University Home Page (http://www.rutgers.edu/).

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Some Commonly Used Gateways

As mentioned above, gateways are computers that sit on two or more networks, passing messages between the networks. They will frequently process an address received from one network into a form acceptable by another. For example, the gateway UK.AC.UCL.CS.NSS automatically reverses the domain ordering on messages passing between JANET and the rest of the Internet.

Usernames on the following networks can be reached in these ways:

• BITnet Rutgers users can reach any BITnet site by using an address in the form:
• user@host.BITNET
• CompuServe For a CompuServe user with the user number 12345,6789, send to
• 12345.6789@COMPUSERVE.COM
• MCIMAIL Send to user-number%MCIMAIL.COM@NRI.RESTON.VA.US
• UUNET Rutgers should be able to reach any host on UUCP directly. However, should the mailer not be able to deliver messages to user@host.uucp, send to user%host.uucp@uunet.uu.net

In general, the best way to reach a user who is not on the Internet is to reply to a message sent to you. You may want to keep one message from such a user in your mail file for that purpose.

Other Questions

Other questions on electronic mail or e-mail addresses can be directed to the OIT/NBCS Help Desk, either in person at Room 005, Hill Center, Busch Campus, by phone at (732) 445-HELP (732-445-4357).

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