E-mail

Electronic mail, sometimes called email, is a computer based method of sending messages from one computer user to another. These messages usually consist of individual pieces of text which you can send to another computer user even if the other user is not logged in (i.e. using the computer) at the time you send your message. The message can then be read at a later time. This procedure is analogous to sending and receiving a letter.
Originally, email messages were restricted to simple text, but now many systems can handle more complicated formats, such as graphics and word processed documents.
When mail is received on a computer system, it is usually stored in an electronic mailbox for the recipient to read later. Electronic mailboxes are usually special files on a computer which can be accessed using various commands. Each user normally has their individual mailbox.
It is straightforward to send electronic mail between users of different computer systems which are connected to major networks. Most major academic and research institutions and companies throughout the world can now be reached by electronic mail. In addition, a growing number of individuals can be contacted in this way.
All email systems have the ability to send, receive and discard mail. Most systems have facilities for storing mail which is to be kept rather than discarded. lt is important to discard mail which does not need to be kept, as it uses storage space on disks. Mailboxes can soon accumulate a large number of mail messages making it difficult to read and process new mail, in addition to wasting disk space.
There is almost always a connection between the email system and the computer’s standard file system which allows mail to be read from files or written to files. This enables greater flexibility in how the mail system is used. For example, a mail message may be prepared in a normal file using a familiar text editor and then sent by the email system. Sections of other files may be included in the mail message as well.
Most systems have a reply facility, although some of these do not always work as expected. Care should be taken when using this facility in electronic mail, as replies do not always go back to the sender.
Mailing lists are supported by many systems. These allow mail which is sent to the name of the list to be sent automatically to all addresses in that list. ln this way mail can be sent to one or more groups of users who share a common interest, e.g. members of a user group or research team, by sending a single message. A number of information services are also available through electronic mail whereby the mail is processed and answered by an automatic process on the remote system.
A mail message consists of a header, which contains information about who the message was sent from, the recipient(s) and the route. Many of the header fields are not shown by default, but most programs used to read email will allow full headers to be displayed. This is then followed by the body of the message which contains whatever the sender wishes. lf the mail message is a formal one, it is customary although not obligatory to finish with your name, return address and other useful information as a signature.
The header consists of lines beginning with a keyword followed by a colon (:), followed by information on each line. A brief explanation of each field of the header is given below. This header contains most of the common fields.
Received: These lines indicate the route that the email has taken and which systems have handled it and the times that it was handled.
Date: The date and time at which the message was sent including time zone.
From: The sender. The part in angle brackets is a real electronic mail address. This field may be user settable, so may not reflect the true sender. In this case, it shows the original sender of the message.
Sender: The sender. This is inserted by some systems if the actual sender is different from the text in the From: field. This makes email more difficult to forge, although this too can be set by the sender. There are other uses for a sender field. In the example above, the sender is set to the list owner by the mailing list system. This allows error messages to be returned to the list owner rather than the original sender of the message.
To: Who the mail is sent to. This may be a list or an individual. However it may bear no relation to the person that the email is delivered to. Mail systems used a different mechanism for determining the recipient of a message.
Cc: Addresses of recipients who will also receive copies.
Subject: Subject of the message as specified by the sender.
Message-ID: A unique system generated id. This can sometimes be useful in fault tracing if multiple copies of a message have been received.
Reply-to: Where any reply should be sent to (in preference to any electronic mail address in the From: field if present). This may be inserted by the sender, usually when they want replies to go to a central address rather than the address of the system they are using. It is also inserted automatically by some systems.
X-Mailer: Any field beginning with X can be inserted by a mail system for any purpose.
When using a reply facility it is important to check where the reply is going by looking at the header of the outgoing message displayed on your screen. If the message has been forwarded to you, the reply will often go to the original sender and not the person who sent it to you.
Electronic mail must be addressed properly, in much the same way as a normal letter needs to be addressed, in order that it can reach its intended recipient. However, with electronic mail the addressing has to be slightly different and must be more precise than a conventional mail address.
Most email uses is addressed using internet addresses. These are supported by what is known as the Domain Name Server (DNS). This is an internationally distributed naming scheme and the components of each address are structured in a hierarchical manner. These start with the mailname of the person, followed by various address components, ending with the ‘Top level’ domain (often a country code). In this respect, the addressing is in the same order as that of a conventional letter.
The mailname comes first, indicating who the email is for. The ‘@’ sign separates the mailname from the site. The next components indicate details of the system to which the email is sent.