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What is Email - Electronic Mail

bullet Introduction

Email is a shorthand term which means: electronic mail. Email, as a term, is also written as e-mail; Ray Tomlinson, the inventor of email said he preferred "email" over "e-mail". Email is similar to a regular postal letter; containing an address, routing information and content. Email uses a range of protocol's - like IMAP, POP3, SMTP - to route messages from mail servers to users. Email predates the Internet: it's first implementation is credited as being the messaging program SNDMSG on the TENEX operating system.

To send and receive email messages a user currently requires an email address; email addresses now depend on DNS and domain names, originally they did not. The majority of Internet Service Providers provide a free email account to customers; likewise, there are a plethora of companies who provide free webmail accounts, such as: Gmail and Yahoo!. Email client programs (like Outlook Express) can be used to access an email account.

Email has proved to be one of the Internet's most popular services, while it has been commended for improving global communications, it has also been criticised for it's security: spam, phishing, viruses and malware are all security issues exasperated by email.

bullet History

Email was not the first electronic messaging system: in 1966, MIT developed the CTSS computer system, and this computer system featured a messaging system similar to Email. CTSS was not the only computer system that featured one-to-one messaging in the 1960's: IBM's Administrative Terminal System and Automatic Digital Network System also featured message systems.

The history of email predates the modern day Internet: a messaging program called SNDMSG was created for the TENEX operating system in the early 1970's, and it's generally recognised as the first email messaging program. SNDMSG allowed users to compose, address, and send an electronic message to a mailbox of other TENEX users. The first message sent on TENEX was sent in 1971, and the program was available by 1972. Ray Tomlinson is credited as it's inventor and the inventor of email.

Ray Tomlinson also worked on the ARPANET Network Control Program - forerunner to TCP/IP and the Internet - therefore, his TENEX email program made a fairly seamless transition to the ARPANET computer network. Ray Tomlinson updated the SNDMSG program with code from the CPYNET program to create the first ARPANET (network capable) email program. Email was immediately popular with ARPANET users, and many Internet pioneers had a 'hand' in it's development: such as Jon Postel, Barry Wessler, Marty Yonke, Larry Roberts, Steve Tepper, Bill Crosby, Steve Walker, Dave Farber, Dave Crocker, and John Vittal; all of whom created early email protocols or programs. Early email applications that built upon SNDMSG and READMAIL included: RD, NRD, WRD, MSG, MS, MH, MMDF and Sendmail.

The FTP protocol was originally used to transport email messages, with FTP commands MLFL and MAIL created to faciliate the SNDMSG program. The first specification of the FTP mail protocol was outlined in RFC 561 by Abhay Bhushan, Ken Pogran, Ray Tomlinson and Jim White. The specification for ARPANET text messages (email) was finally formalised in 1977 (RFC 733) by David H. Crocker, John J. Vittal, Kenneth T. Pogran and D. Austin Henderson, Jr.

Only at a late date were standalone protocols developed for email, such as: IMAP, X400, POP, SMTP, and UUCP. The most important email protocol is SMTP: developed in the early 1980's and outlined in RFC 821 (1982) by Jonathan B. Postel; it is still in use today. POP was the next 'core' email protocol developed, outlined in RFC 918 (1984) by J. K. Reynolds. The 'holy trinity' of email protocols was finialised in 1986, when Mark Crispin developed IMAP; and updated it's specification for decades in RFC documents RFC 1064, RFC 2060 and RFC 3501. Some email protocols have become obsolete: such as Jon Postel's Mail Transfer Protocol (MTP). Present day, most email systems rely on either: SMTP, POP or IMAP.

The key features of an email message have remained the same: comprising a header and a body. The syntax of a email address has also remained the same: Ray Tomlinson being the inventor of using the @ symbol in 1972. While email was initially used by academic researchers and the military, by the late 1980's Vinton Cerf had faciliated commerical access, and by the early 1990's - when commercial networks controlled the backbone of the Internet - commercial providers like AOL ensured that it would become the Internet's most popular service.

bullet Format of an Email message

The email message format has largely remained the same since Ray Tomlinson sent the first email in 1971, however, it has evolved and it's message format specification has been outlined in the following RFC documents: RFC733, RFC822, RFC1342, RFC1521, RFC1522, RFC1590, RFC2045, RFC2046, RFC2047, RFC2048, RFC2049, RFC2822, RFC4021, and RFC5322. Important contributors to the format of email messages include: P. Resnick, G. Klyne, J. Palme, David H. Crocker, John J. Vittal, N. Borenstein, N. Freed, K. Moore, J. Postel, Kenneth T. Pogran and D. Austin Henderson, Jr.

The format of email messages is broken into two sections: 1) a header, 2) message body. (read more on the header and body)

The header of an email message is more complex than the body, because it contains the information needed to encode and route the email message. The header section contains lines of instructions, which are referred to as "header identifiers". The primary role of these identifiers is to provide routing commands for mail transfer agents (which play the online role of a postal service). Some of these identifiers are mandatory for an email message; which basically means the email message cannot be sent without them: the following identifiers are mandatory: From: and Date:. Alongside the mandatory header identifiers, there are a plethora of identifiers which deal with the cosmetic aspects of the email. Listed below, is the typical identifiers you will find in an email header:

The Cc: field is used to send a message to multiple additional addresses (Bcc: field hides the addresses from other recipients) and the Subject: field is used to describe what is included in the body of the message. Email headers sometimes contain two or more of the same identifiers, usually the "received" and "date" identifiers: which are added to the header by each mail transfer agent that handles the message.

The body section of an email message is far less complex: as it contains the content of the message. Originally the content of email's was only plain text (7-bit ASCII), and some mail servers still only support plain text email messages. However, if the content type of the email (included in the header) includes a MIME field: then the body of the email message can be encoded with non-ASCII data such as HTML elements. Therefore, the body section of an email message can then include plain text and HTML content. The drawback to HTML emails is that faciliate an increase of phishing attacks and increased the risk of users being infected with malware. Plain text emails are far more secure.

bullet Anatomy of an Email address

The syntax of an email address has changed over time: historical addresses existed before the Domain Name System (DNS) and DNS domain names are currently an essential component of modern email addresses. Historical email addresses relied on the ability of servers being able to connect directly to one another; DNS was developed, in part, to solve this unwieldy and clumsy design issue. That said, the syntax of an email address has largely remained the same - since the first email format - and can be broken down into three sections:

tom@example.com: 1. tom 2. @ 3. example.com

The first section of the email address is the username (tom) which refers to the recipient's account name at a mail service; also referred to as the 'local' part of an email address. The username of an email address is locally unique but is not globally unique: the username (tom) can be used at an unlimited amount of mail servers: tom@example.com, tom@example2.com, tom@example3.com etc.

The second section of an email address is the @ sign - which is included in every email address - and means 'at' and connects the local part of the email address to the hostname of the email address. The use of this symbol dates back to the first ever email message, and the use of the symbol was invented by Ray Tomlinson.

The third section of an email address is the hostname (internet-guide) - which is a domain name - that is associated with a mail server. Domain names are part of the Domain Name System (DNS): an Internet naming system that converts alphanumeric domain names into an IP address; so that users can easily find the address of Internet resources. Domain names are connected to mail servers through the DNS MX record field. The domain name of an email address includes two (or more) sections: example.com has a second level domain (example) and a top level domain (com). The second level domain can be registered through DNS registrars, which enables users to have a personalised email address rather than a universal one, such as: yahoo.com, aol.com, hotmail.com, mail.com etc. There are currently over 1000 top level domains, such as: com, org, net, uk, fr, gr, info, mil, gov and edu.

When sending an email message it is essential to spell the email address correctly; just as with a normal postal letter. If the email address is spelt incorrectly, then it will not be sent to the correct location. If an email message is sent to an address that does not exist: then the message will be returned with an "Address Unknown" error.

bullet Email: transfer, retrieval and storage

Email messages are transferred from one computer to another using software named a Mail Transfer Agent (MTA); also referred to as a Mail Relay. MTAs implement the Simple Mail Transfer Protocol (SMTP) and mail servers are the computers that use MTA software. MTAs are sometimes referred to as mail server programs; Sendmail and Microsoft Exchange Server are two examples of an MTA. SMTP sessions use commands like: DATA, EXPN, HELO, HELP, MAIL, NOOP, QUIT, RCPT, RSET and VRFY - beginning with HELO, transacting with MAIL and ending with QUIT. You can learn more about the SMTP protocol by reading Request for Comments documents 'RFC 5322' and 'RFC 5321'.

Email is built upon a client server model: the Mail Transfer Agent (MTA) receives mail from a Mail User Agent (MUA) (client program like Outlook Express), another Mail Transfer Agent (MTA), or a Mail Submission Agent (MSA) (outgoing mail server). How the mail is transported is specified by SMTP. The header section of an email message (received field) will list the MTAs that have handled the email message. Email addresses contain a domain name that is linked to a mail server - through the DNS MX record field - and this will dictate where an email message is sent and received.

Once the email has been transported and reaches the Message Delivery Agent (MDA) it then needs to be stored in a mailbox. There are many formats that can handle mailbox storage, perhaps the most simple and efficient is Maildir. Maildir operates by creating unique temporary files for each retrieved message. It will depend on the client or webmail, as to which storage format they will use; Maildir, for example, was designed for the qmail program, but is compatible with other clients. Not all storage formats create unique files for each e-mail; another option is to use a collective database format; mBox is one such example, storing messages in one single file. Why are there a variety of different techniques for storing messages? unlike message transfer, the Internet Engineering Task Force (IETF) has not developed a standard mechanism for storage.

Email messages are typically retrieved by a Mail User Agent (MUA) using the Post Office Protocol (POP3) orthe Internet Message Access Protocol (IMAP); although there are other protocols that fulfil this role.

A rough outline of the Email process, step by step:

  1. A sender composes an email message in a Mail User Agent (MUA).
  2. The Mail User Agent (MUA) then formats the message in an SMTP format.
  3. The email message is sent to a local MTA.
  4. The MTA reads the destination address using the domain address in the email address 'joe@example.com'.
  5. The MTA will lookup the mail server address using the DNS MX record field of the domain name.
  6. The DNS system will give the MTA the 'mail exchange server' for the domain.
  7. The MTA will send the email onto the mail exchange server using SMTP.
  8. The email message will arrive at the Message Delivery Agent (MDA) that will store the message in the users mailbox.
  9. The users Mail User Agent (MUA) will use POP or IMAP to retrieve the message from the mailbox.
bullet Webmail Accounts

Webmail, as the name would suggest, is an email service that is accessed through the World Wide Web. The World Wide Web was launched as an Internet service in 1991, whereas email was invented in the early 1970's. Therefore, webmail is a relatively new development for email; before webmail, most users accessed email through a standalone email client application (Mail User Agent (MUA)) like Eudora. Webmail uses the same email protocols as earlier email clients, the only difference is the way in which the email account is accessed.

There are a plethora of free email accounts available from webmail providers, such as: hotmail. While early webmail services were criticised for a lack of protection versus email bombs, spam and flooding, modern webmail services provide protection against these abuses. Professional webmail services provide additional features, alongside the obvious features, such as: attachments, blind carbon copy options, e-cards, encryption and decryption. Every type of webmail account should be able to receive e-zines and newsletters.

The drawback with free webmail accounts is that the user cannot pick a unique domain name: instead they are stuck with domain name of the service provider: such as yahoo.com. However, user can pick an individual 'username' to suit their purposes. If a user wants an email address with a unique domain name - they can access the inbox with a client program - then they will have to purchase that domain name and host it with a company that provides support for email protocols.

bullet Frequently Asked Questions

bullet When was Email created / invented?
bullet Does Email have a standard format?
bullet How big can email attachments be?
bullet Is encryption available for email messages?
bullet What is spoofing in relation to email messages?
bullet What does it mean: bombing an email account?
bullet Password tips for UK email accounts
bullet Why do email services supply an anti-virus scanner?
bullet Does a spam filter offer effective spam protection?
bullet What is meant by a phishing attempt via email?
bullet Jamming: sensitive words inserted into an email
bullet Mule email account: avoiding spam and a loss of privacy
bullet Is Phil Zimmerman the developer of an email encryption program?
bullet How to secure my email account after it has been hacked?
bullet Is it easy to terminate an email account?
bullet How to safeguard and protect an email account
bullet Are OpenID and Webmail related?
bullet Is it possible to block emails?
bullet Why do email providers want my mobile number?
bullet Can I import my contacts into a new email account?