Electronic mail(e-mail)

Electronic mail, often abbreviated as email, e.mail or e-mail, is a method of exchanging digital messages, designed primarily for human use. E-mail systems are based on a store-and-forward model in which e-mail computer server systems accept, forward, deliver and store messages on behalf of users, who only need to connect to the e-mail infrastructure, typically an e-mail server, with a network-enabled device (e.g., a personal computer) for the duration of message submission or retrieval. Originally, e-mail was always transmitted directly from one user's device to another's; nowadays this is rarely the case.

An electronic mail message consists of two components, the message header, and the message body, which is the email's content. The message header contains control information, including, minimally, an originator's email address and one or more recipient addresses. Usually additional information is added, such as a subject header field.

Originally a text-only communications medium, email was extended to carry multi-media content attachments, which were standardized in with RFC 2045 through RFC 2049, collectively called, Multipurpose Internet Mail Extensions (MIME).

The foundation for today's global Internet e-mail service was created in the early ARPANET and standards for encoding of messages were proposed as early as, for example, in 1973 (RFC 561). An e-mail sent in the early 1970s looked very similar to one sent on the Internet today. Conversion from the ARPANET to the Internet in the early 1980s produced the core of the current service.

Network-based email was initially exchanged on the ARPANET in extensions to the File Transfer Protocol (FTP), but is today carried by the Simple Mail Transfer Protocol (SMTP), first published as Internet standard10 (RFC 821) in 1982. In the process of transporting email messages between systems, SMTP communicates delivery parameters using a message envelope separately from the message (headers and body)

Why use email?

The operating principle behind email is relatively simple, which has quickly made it the most popular service used on the Internet.

As with a traditional postal service, for your message to reach your recipient, all you need to know is their address. Its two main advantages over "paper mail" are the speed at which the email is sent (practically instantaneous) and the lower cost (included with the cost of an Internet connection).

What's more, email can be used to instantaneously send a message to several people at once.

Email addresses

Email addresses (both for senders and recipients) are two strings separated by the character "@" (the "at sign"):

user@domain

The right-hand part describes the domain name involved, and the left-hand part refers to the user who belongs to that domain. One or more mail servers (MX records in the Domain Name System) correspond to each domain.

An email address can be up to 255 characters long and can include the following characters:

• Lowercase letters from a to z;
• Digits
• The characters ".","_" and "-" (full stop, underscore, and hyphen)

In practice, an email address often looks something like this:

firstname.lastname@provider.domain

Email, as simple as it is to use, relies on a more complicated set of operating procedures than that of the Web. For most users, its operation is transparent, which means that it is not necessary to understand how email works in order to be able to use it.
However, the short introduction below has been provided to help users understand its basic principles, give them an idea of how to best configure their email clients and inform them about the underlying mechanisms of spam.
How email works
Email is based around the use of electronic mailboxes. When an email is sent, the message is routed from server to server, all the way to the recipient's email server. More precisely, the message is sent to the mail server tasked with transporting emails (called the MTA, for Mail Transport Agent) to the recipient's MTA. On the Internet, MTAs communicate with one another using the protocol SMTP, and so are logically calledSMTP servers (or sometimes outgoing mail servers).
The recipient's MTA then delivers the email to the incoming mail server (called the MDA, for Mail Delivery Agent), which stores the email as it waits for the user to accept it. There are two main protocols used for retrieving email on an MDA:
POP3 (Post Office Protocol), the older of the two, which is used for retrieving email and, in certain cases, leaving a copy of it on the server.
IMAP (Internet Message Access Protocol), which is used for coordinating the status of emails (read, deleted, moved) across multiple email clients. With IMAP, a copy of every message is saved on the server, so that this synchronisation task can be completed.
For this reason, incoming mail servers are called POP servers or IMAP servers, depending on which protocol is used.
To use a real-world analogy, MTAs act as the post office (the sorting area and mail carrier, which handle message transportation), while MDAs act as mailboxes, which store messages (as much as their volume will allow) until the recipients check the box. This means that it is not necessary for recipients to be connected in order for them to be sent email.
To keep everyone from checking other users' emails, MDA is protected by a user name called a login and by a password.
Retrieving mail is done using a software program called an MUA (Mail User Agent).
When the MUA is a program installed on the user's system, it is called an email client (such as Mozilla Thunderbird, Microsoft Outlook, Eudora Mail, Incredimail or Lotus Notes).
When it is a web interface used for interacting with the incoming mail server, it is called webmail.
Open relay
By default, and for historical reasons, it is not necessary to authenticate oneself to send email, which means that it is very easy to falsify one's own address when sending mail.
For this reason, nearly all Internet service providers lock down their SMTP servers to that only their subscribers can use them, or more precisely only machines whose IP address belongs to the ISP's domain. This explains why travelling users must modify the outgoing server settings in their email clients each time they move to a new home or business.
When an organisation's email server is improperly configured and allows third-party users on any network to send emails, this is called an open relay.
Open relays are generally used by spammers, as using them hides the true origins of their messages. As a result, many ISPs keep an up-to-date blacklist of open relays, to keep subscribers from receiving messages from such servers. 

sing email
An email client, a software program for writing, checking and sending email, is generally made up of a number of windows. The main windows of this software are:
Incoming, In, Inbox: This represents the main mailbox for receiving email,
Sent, Outbox, Out: These are copies of messages that you have sent.
Deleted, Trash: The trash bin containing deleted emails. When emails are shown in the trash, you can still retrieve them. To permanently delete them, you will need empty the trash bin.
Folders: Most clients can be used to file emails in folders, much like folders on a hard drive.
Email fields
Here are the meanings of the fields to be filled in when you send an email:
From: this is your email address; most of the time you will not have to fill in this field, because it is generally set by the email client according to your preferences.
To: This field is used for the recipient's email address.
Subject: this is the title that your recipients will see when they want to read the email
Cc (carbon copy): this allows an email to be send to a large number of people by writing their respective addresses separated by commas
Bcc (blind carbon copy): This is a Cc, except that the recipient does not see the list of people in the Bcc field
Message: This is the body of your message
The Carbon Copy function sends a copy to people not directly involved with the message but whom you wish to keep up to date with the message contents or show that you sent the email to the recipient(s).
The Blind Carbon Copy function makes it possible to forward messages without any of the recipients or even the hidden recipients seeing that the message is being forwarded to them. It is generally recommended when sending an email to many people to forward it using Blind copy so as to prevent one of the recipients from replying to everyone or assembling a list of addresses.
Other email functions are:
Attached Files, Attachments: A file can be attached to an email by specifying its location on the hard drive.
Signature: If the email client allows it, you are often able to set a signature, meaning a few lines of text which will be added to the end of the document.
What to do with a message
There are many operations that can be performed on emails:
New, Compose, Write: Write a new message
Erase, Delete, Remove: Erase a message
Store, Save, Backup, Drafts: Copy a message into a safer place
Print: Print a message
Reply: Send a reply message to the sender (sometimes including their own message in the body of the document, with each line preceded by the symbol ">" and "Re:" followed by their chosen subject as the title, to show that it is a reply. The Reply All button makes it possible to send a reply to the sender as well as everyone else who had been put as a recipient or on copy.
Forward: Forwards the message to someone else, letting them know that the message comes from you. The subject is generally preceded by Fwd: to indicate that it is a forwarded message.
Redirect, Transmit: Forward a message to someone, letting them know where it originally came from. The subject is generally preceded by Fwd: to indicate that it is a forwarded message.
Netiquette
Netiquette (a contraction of the words "Net" and "etiquette") refers to the set of rules governing correct behaviour on the Internet, in order to respect others and be respected in turn.
They serve as guidelines for civility and proper conduct, so that all users can act in a like manner respectful of others.
When composing and sending a message
Indicate the subject of the message clearly in the "Subject" field. This is particularly critical for the recipient If the message's subject is explicit, it will make it much easier for the recipient, when looking at all the emails received, to tell which ones are most important and which less so. This will also allow the recipient to easily sort out their mail. You can make a distinction between a general subject, normally placed within brackets (such as for the name of a project) and a short summary of the message; for example:
[Project X] Meeting on 13 December
Only send email to people who are involved - It is ill-advised, and annoying for recipients, to send email to anyone you know. Recipients waste valuable time sorting out the messages which actually involve them from those which they have little or no interest in. What's more, this practice needlessly ties up network resources.
The "To:" field designates the primary recipient. This is the person to whom the email is addressed.
The "Cc:" field designates people who are being kept informed about this email communication.
The "Bcc:" field designates recipients whom the other recipients cannot see. It is recommended to not use this feature. Instead, it is advisable to separately forward them a copy of the preceding message.
Be brief and give ample context for the message. To be read and understood, it is preferable to use short, precise sentences. If the message is long, divide it into multiple paragraphs to make it easier to read. A precise, well-structured text helps prevent misunderstandings or misinterpretations. A message can be quickly and easily forwarded to other users. Use suitable language, and avoid misplaced humour, sarcasm, and insults. For the benefit of recipients in professional settings, it is helpful to begin a message with one of the following phrases:
For your information
For your approval
Follow-up
If documents must be attached to the message, take the recipients into consideration. The recipient of an attached file might not have the software to read it. Make sure that the file is saved in a format which most current software can read. (e.g. .rtf instead of .doc). Additionally, be aware of the attachment's size. The larger the size of the file, the longer it will take to send and receive. A hefty attachment might be blocked by the remote email server, or fill up the recipient's inbox, preventing other messages from being received. Use compression/decompression utilities (such as ZIP) to reduce the size of these files.
Before sending a message which is supposed to contain an attachment, make sure that the attachment is really there!
Avoid using uppercase letters. Text written in uppercase is difficult to read. What's more, using words in all capital letters on the Internet indicates that you are expressing strong emotions (such as joy or anger), which the recipient of your message might not take well. To emphasise a term, place it in quote marks instead.
Before sending a message, take the time to reread it. Try correcting typos or language errors. The style of the message reflects the sender's image.
Make sure you identify yourself, and leave contact information at the end of the message. Consider leaving your signature at the bottom of your emails, but without taking up too much space (four or five lines at the most), specifying, e.g. your occupation and the organisation you belong to. Telephone numbers may be useful if one of the recipients needs to contact you quickly. Custom dictates that the signature be preceded by a line containing nothing but two dashes ("--").
When receiving a message
When a message has been read, decide immediately where to file it. Email can be managed just like traditional mail. To find a message easily, make a habit of filing the messages you receive into folders by topic. This way, it will be easier to find an old message or discussion thread. Some email clients let you assign a colour to a message. It may be useful to set a colour code for identifying certain categories of messages.
Except where necessary, do not print out emails. When email is filed properly, it may be easily found if needed. For this reason, it is useless to print out every email. This prevents wasting paper, helping to preserve the environment.
Respect the private nature of the messages you receive. Never forward or copy to others an email personally addressed to you without the consent of the original sender.
On using emoticons (smileys)
Emoticons (sometimes called smileys) are symbols included in messages to indicate the mood of the person who wrote the message (humourous, sarcastic, ironic, etc.) Their use is normally reserved for non-professional messages.
To create an emoticon, simply use punctuation symbols. To see them more easily, tilt your head 90 degrees to the left. 
Concept of mailing lists
A mailing list is one of the most commonly used services on the Internet, allowing people to send messages to one or more recipients. Email was invented by Ray Tomlinson in 1972.
Mailing list managers
A mailing list is based around software called a mailing list manager (or MLM for short).
This software distributes emails to all subscribers. It must properly handle bounced emails, as well as addresses which are not responding. If a user on the list has programmed an away message, the mailing list manager and that user's email client might send messages back and forth to one another, leading to an unending chain of emails.
An MLM also responds to commands found in the subject or body of the email. Here are a few example commands which most mailing list managers understand:
SUBSCRIBE: used for requesting a subscription to the list
UNSUBCRIBE: used for unsubscribing from the list
HELP: requests that the MLM list all commands available
Discussion list/Mailing list
The mailing list manager is generally administered by a list administrator whose job is to keep the lists in good working order and configure them as needed. Some lists may be moderated, meaning that every message shared must first be approved by a moderator to be transmitted to the list.
A list's administrator can decide if the subscribers may or may not respond to messages, if list membership is open to all. When the subscribers can reply to the list, it is called a "discussion list".

Structure of an email
An email has three basic parts:
The header, a set of lines containing information about the message's transportation, such as the sender's address, the recipient's address, or timestamps showing when the message was sent by intermediary servers to the transport agents (MTAs), which act as a mail sorting office. The header begins with a From line and is changed each time it passes through an intermediary server. Using headers, you can see the exact path taken by the email, and how long it took each server to process.
The message proper, made up of the two following elements:
the header fields, a set of lines describing the message's settings, such as the sender, the recipient, the date, etc. Each one has the following form:
Name: Value
An email includes at least the three following headers:
From: The sender's email address
To: The recipient's email address
Date: The date when the email was sent
It may contain the following optional fields:
Received: Various information about the intermediary servers and the date when the message was processed.
Reply-To: A reply address.
Subject: The message's subject
Message-ID: A unique identification for the message.
the message body, containing the message, separated from the header by a line break.
An email is made up of lines of displayable 7-bit US-ASCII characters. Each line has at most 76 characters, for compatibility reasons, and ends with the characters CRLF (\r\n).
Concept of a header
It is important to note that header data is no guarantee of when the message was sent or who sent it.
Additional personalised headers (called X-headers) can be set in order to provide the appropriate information. X-headers are so called because their name must begin with X-.
Some anti-spam software programs mark messages as unwanted using the following header:
X-Spam-Status: Yes