Electronic mail addresses in general contain two parts, identifying in some way the person and the location, similar to a postal address for paper mail. The form is user@host, where user identifies the person and host the location. In fact, there may be more behind it; the user may be an alias for another address or for a list, and the host may re-send the message to another place.
You can address other users on them simply by userid. For example, to send to the userid jb51, just type the userid.
MM>send To: jb51
When you read mail from other users on your own system, you will notice that the address has usually been expanded into full Internet domain form, as explained below. The mail system does that for you.
For all other cases, you must add an at-sign (@) and a hostname. The easiest way to get someone's address is to ask them what it is by telephone or paper mail. If you get mail from someone, note the address in the From line. Some sites have directories that you can query by the finger or whois commands, or by using a gopher.
Mail to or from outside locations goes through a computer network. Many regional computer networks around the world are interconnected to form what is known in the aggregate as the Internet. A second major network for academic users is BITNET. Users are not normally charged per message, but rather the sites pay to support their connection to the local part of the Internet and possibly BITNET.
This address uses the Domain Name System that is the most common way to write addresses on the Internet. The host name is made up of at least two parts separated by periods. The address itself may be accompanied by a real name or other comment, as in the second line above
The last part is called the Top Level Domain, and indicates the country (outside the US) or type of site (in the US). Probably you will see .edu (educational in US) and .com (commercial in US) the most frequently. Preceding parts indicate the site and local systems at the site.
This is an alternative to the above, allowing use of the person's real name or some other phrase together with the address itself in < > brackets. This form is useful for mailing lists, to help you recall who each address is. You will see MM using this form in From lines. Another form that is falling out of use would be to write the address followed by the name or phrase in ( ) parentheses.
This is the alternate form of address on the Internet, an IP number address. Note the use of square brackets. The name form (above) is preferable.
This is a common way to write a BITNET address on an Internet site. The BITNET address proper is just xyz@matrix and the .bitnet is an instruction to the mail system to deliver the message via BITNET. In BITNET terminology the host matrix is referred to as a node.
The alternative way to write the address would be to specify an Internet site that will pass the message into BITNET, for example, firstname.lastname@example.org. You may see this in some From lines and use it when you send a reply to such a message.
An older style of addressing uses a bang path (named for the ! marks) to list the hosts the mail has to pass through to reach the user, who is the last element in the path. In some cases this is now used for non-Internet mail-only connections, as shown above, where the mail appears to go to some.edu and then via host foo to user baz on a host named bar.
This is an address on the JANET network in England, but written in Internet domain form. Within England, host names are written in reverse (from our point of view), like uk.ac.oxford.bigvax. You may need to reverse addresses you are given for the UK so that uk is at the end.
This is just one example of a gateway to another network, in this case the commercial network Compuserve. Generally, write the address in the network's own format followed by @ and the Internet address of the gateway site. Sometimes the non-Internet address needs to be slightly modified, as here the Compuserve 70123,4567 needs the comma changed to a period. Contact postmaster for more information on gateways.
To save typing long addresses, you can use the define command to define a nickname for a long address, and then use the nickname when you send mail.
You can send questions about addresses to postmaster, a system alias for staff who are expert in mail problems. Typical problems involve routing mail to other networks or determining why mail was returned undelivered. Most sites on the Internet have a postmaster who can be reached as postmaster@host, if you know the host name for a site.