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Electronic mail, most commonly called email or e-mail since around 1993, is a method of exchanging digital messages from an author to one or more recipients. Email operates across the or other .

Some early email systems required the author and the recipient to both be at the same time, in common with . Today's email systems are based on a model. Email accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simultaneously; they need connect only briefly, typically to a , for as long as it takes to send or receive messages.

Historically, the term electronic mail was used generically for any electronic document transmission. For example, several writers in the early 1970s used the term to describe document transmission.Ron Brown, Fax invades the mail market, New Scientist, Vol. 56, No. 817 (Oct., 26, 1972), pages 218–221.Herbert P. Luckett, What's News: Electronic-mail delivery gets started, Popular Science, Vol. 202, No. 3 (March 1973); page 85 As a result, it is difficult to find the first citation for the use of the term with the more specific meaning it has today.

An Internet email message consists of three components, the message envelope, the message header, and the message body. The message header contains control information, including, minimally, an originator's and one or more recipient addresses. Usually descriptive information is also added, such as a subject header field and a message submission date/time stamp.

Originally an text-only communications medium, Internet email was extended by (MIME) to carry text in other character sets and multi-media content attachments. , with internationalized email addresses using , has been standardized, but not yet widely adopted.

Electronic mail predates the inception of the Internet and was in fact a crucial tool in creating it, but the history of modern, global Internet email services reaches back to the early . Standards for encoding email messages were proposed as early as 1973 (RFC 561). Conversion from ARPANET to the Internet in the early 1980s produced the core of the current services. An email message sent in the early 1970s looks quite similar to a basic text message sent on the Internet today.

Email is an . It uses technology to communicate a digital message over the Internet. Users use email differently, based on how they think about it. There are many software platforms available to send and receive. Popular email platforms include Gmail, Hotmail, Yahoo! Mail, Outlook, and many others.

Network-based email was initially exchanged on the ARPANET in extensions to the (FTP), but is now carried by the (SMTP), first published as 10 (RFC 821) in 1982. In the process of transporting email messages between systems, SMTP communicates delivery parameters using a message envelope separate from the message (header and body) itself.

Electronic mail has several English options:
  • email is the most common form used online, and is required by and working groups This is suggested by the RFC Document Style Guide and increasingly by . AP Stylebook editors share big changes from the This spelling also appears in most dictionaries.Random House Unabridged Dictionary, 2006The American Heritage Dictionary of the English Language, Fourth EditionPrinceton University WordNet 3.0The American Heritage Science Dictionary, 2002
  • e-mail has long been the form that appears most frequently in edited, published American English and British English writing as reflected in the data and style guides.
  • mail was the form used in the original RFC. The service is referred to as mail, and a single piece of electronic mail is called a message.
  • EMail is a traditional form that has been used in RFCs for the "Author's Address" and is expressly required "for historical reasons".
  • E-mail is sometimes used, capitalizing the initial E as in similar abbreviations like , , , and .

The network, first operational in 1962, provided a message service between 1,350 terminals, handling 30 million messages per month, with an average message length of approximately 3,000 characters. Autodin was supported by 18 large computerized switches, and was connected to the Advanced Record System, which provided similar services to roughly 2,500 terminals.USPS Support Panel, Louis T Rader, Chair, Chapter IV: Systems, Electronic Message Systems for the U.S. Postal Service, National Academy of Sciences, Washington, D.C., 1976; pages 27–35.

Host-based mail systems
With the introduction of 's (CTSS) in 1961"CTSS, Compatible Time-Sharing System" (September 4, 2006), , USA-CTSS. multiple users were able to log into a central systeman from remote dial-up terminals, and to store and share files on the central disk., "The IBM 7094 and CTSS" (September 10, 2004),
([[Multics]]), web: [ Multicians-7094]. Informal methods of using this to pass messages were developed and expanded :

Developers of other early systems developed similar email applications:

These original messaging systems had widely different features and ran on systems that were incompatible with each other. Most of them only allowed communication between users logged into the same host or "mainframe", although there might be hundreds or thousands of users within an organization.

LAN email systems
In the early 1980s, networked on became increasingly important. Server-based systems similar to the earlier mainframe systems were developed. Again, these systems initially allowed communication only between users logged into the same server infrastructure. Examples include: Eventually these systems too could link different organizations as long as they ran the same email system and proprietary protocol.with various vendors supplying gateway software to link these incompatible systems

Email networks
To facilitate electronic mail exchange between remote sites and with other organizations, telecommunication links, such as dialup modems or leased lines, provided means to transport email globally, creating local and global networks.
  • In 1971 the first email was sent, and through RFC 561, RFC 680, RFC 724, and finally 1977's RFC 733, became a standardized working system.
  • PLATO IV was networked to individual terminals over leased data lines prior to the implementation of personal notes in 1974.
  • Unix mail was networked by 1978's , which was also used for newsgroup postings, with similar headers
  • BerkNet, the Berkeley Network, written by in 1978 and included first in the Second Berkeley Software Distribution provided support for sending and receiving messages over serial communication links. The Unix mail tool was extended to send messages using BerkNet.
  • The tool written by in 1979 and 1980 (and shipped in 4BSD) provided support for routing mail over different networks including Arpanet, UUCP, and BerkNet. (It also provided support for mail user aliases.)Setting up the Fourth Berkeley Software Tape, William N. Joy, Ozalp Babaoglu, Keith Sklower, University of California, Berkeley, 1980.
  • The mail client included in 4BSD (1980) was extended to provide interoperability between a variety of mail systems.Mail(1), UNIX Programmer's Manual, 4BSD, University of California, Berkeley, 1980.
  • (1981) provided electronic mail services for educational institutions. It was based on the IBM VNET email system. "BITNET History",
  • In 1984, IBM PCs running DOS could link with for email and shared bulletin board posting.

Attempts at interoperability
Early interoperability among independent systems included: Network World
but abandoned it after purchasing the non-MHS WordPerfect Office (renamed )
  • The on academic networks until 1992
  • in the 1980s and early 1990s was promoted by major vendors, and mandated for government use under , but abandoned by all but a few in favor of by the mid-1990s.

In the early 1970s, Ray Tomlinson updated an existing utility called so that it could copy messages (as files) over the network. The project manager for the ARPANET development, took the idea of READMAIL, which dumped all "recent" messages onto the user's terminal, and wrote a programme for in macros called RD, which permitted access to individual messages. Barry Wessler then updated RD and called it NRD.*

Marty Yonke rewrote NRD to include reading, access to SNDMSG for sending, and a help system, and called the utility WRD, which was later known as BANANARD. John Vittal then updated this version to include three important commands: Move (combined save/delete command), Answer (determined to whom a reply should be sent) and Forward (sent an email to a person who was not already a recipient). The system was called MSG. With inclusion of these features, MSG is considered to be the first integrated modern email programme, from which many other applications have descended.

Experimental email transfers between separate computer systems began shortly after the creation of the in 1969. is generally credited as having sent the first email across a network, initiating the use of the "" sign to separate the names of the user and the user's machine in 1971, when he sent a message from one computer to another DEC-10. The two machines were placed next to each other.Wave New World,Time Magazine, October 19, 2009, p.48 Tomlinson's work was quickly adopted across the ARPANET, which significantly increased the popularity of email.

Initially addresses were of the form, username@hostnameRFC 805, 8 February 1982, Computer Mail Meeting Notes but were extended to "username@host.domain" with the development of the (DNS).

As the influence of the ARPANET spread across academic communities, were developed to pass mail to and from other networks such as , , , , and . This often involved addresses such as:

which routes mail to a user with a "" address at a UUCP host.

The diagram to the right shows a typical sequence of events that takes place when sender transmits a message using a (MUA) addressed to the of the recipient.
  1. The MUA formats the message in email format and uses the submission protocol, a profile of the (SMTP), to send the message to the local (MSA), in this case
  2. The MSA determines the destination address provided in the SMTP protocol (not from the message header), in this case The part before the @ sign is the local part of the address, often the of the recipient, and the part after the @ sign is a . The MSA resolves a domain name to determine the fully qualified domain name of the in the (DNS).
  3. The for the domain ( responds with any listing the mail exchange servers for that domain, in this case, a (MTA) server run by the recipient's ISP. "MX Record Explanation",
  4. sends the message to using SMTP. This server may need to forward the message to other MTAs before the message reaches the final (MDA).
  5. The MDA delivers it to the of user bob.
  6. Bob's MUA picks up the message using either the (POP3) or the (IMAP).

In addition to this example, alternatives and complications exist in the email system:

  • Alice or Bob may use a client connected to a corporate email system, such as or . These systems often have their own internal email format and their clients typically communicate with the email server using a vendor-specific, proprietary protocol. The server sends or receives email via the Internet through the product's Internet mail gateway which also does any necessary reformatting. If Alice and Bob work for the same company, the entire transaction may happen completely within a single corporate email system.
  • Alice may not have a MUA on her computer but instead may connect to a service.
  • Alice's computer may run its own MTA, so avoiding the transfer at step 1.
  • Bob may pick up his email in many ways, for example logging into and reading it directly, or by using a webmail service.
  • Domains usually have several mail exchange servers so that they can continue to accept mail even if the primary is not available.

Many MTAs used to accept messages for any recipient on the Internet and do their best to deliver them. Such MTAs are called . This was very important in the early days of the Internet when network connections were unreliable. However, this mechanism proved to be exploitable by originators of and as a consequence open mail relays have become rare, and many MTAs do not accept messages from open mail relays.

Message format
The Internet email message format is now defined by RFC 5322, with multi-media content attachments being defined in RFC 2045 through RFC 2049, collectively called or MIME. RFC 5322 replaced the earlier RFC 2822 in 2008, and in turn RFC 2822 in 2001 replaced RFC 822 – which had been the standard for Internet email for nearly 20 years. Published in 1982, RFC 822 was based on the earlier RFC 733 for the .

Internet email messages consist of two major sections, the message header and the message body. The header is structured into such as From, To, CC, Subject, Date, and other information about the email. The body contains the message, as unstructured text, sometimes containing a at the end. The header is separated from the body by a blank line.

Message header
Each message has exactly one , which is structured into . Each field has a name and a value. RFC 5322 specifies the precise syntax.

Informally, each line of text in the header that begins with a begins a separate field. The field name starts in the first character of the line and ends before the separator character ":". The separator is then followed by the field value (the "body" of the field). The value is continued onto subsequent lines if those lines have a space or tab as their first character. Field names and values are restricted to 7-bit characters. Non-ASCII values may be represented using MIME .

Header fields
Email header fields can be multi-line, and each line should be at most 78 characters long and in no event more than 998 characters long. Header fields defined by RFC 5322 can only contain characters; for encoding characters in other sets, a syntax specified in RFC 2047 can be used. Recently the IETF EAI working group has defined some standards track extensions, replacing previous experimental extensions, to allow encoded characters to be used within the header. In particular, this allows email addresses to use non-ASCII characters. Such characters must only be used by servers that support these extensions.

The message header must include at least the following fields:

  • From: The , and optionally the name of the author(s). In many email clients not changeable except through changing account settings.
  • Date: The local time and date when the message was written. Like the From: field, many email clients fill this in automatically when sending. The recipient's client may then display the time in the format and time zone local to him/her.

The message header should include at least the following fields:

  • Message-ID: Also an automatically generated field; used to prevent multiple delivery and for reference in In-Reply-To: (see below).
  • In-Reply-To: of the message that this is a reply to. Used to link related messages together. This field only applies for reply messages.

RFC 3864 describes registration procedures for message header fields at the ; it provides for permanent and provisional message header field names, including also fields defined for MIME, netnews, and http, and referencing relevant RFCs. Common header fields for email include:

  • To: The email address(es), and optionally name(s) of the message's recipient(s). Indicates primary recipients (multiple allowed), for secondary recipients see Cc: and Bcc: below.
  • Subject: A brief summary of the topic of the message. are commonly used in the subject, including .
  • Bcc: ; addresses added to the SMTP delivery list but not (usually) listed in the message data, remaining invisible to other recipients.
  • Cc: ; Many email clients will mark email in one's inbox differently depending on whether they are in the To: or Cc: list.
  • : Information about how the message is to be displayed, usually a type.
  • Precedence: commonly with values "bulk", "junk", or "list"; used to indicate that automated "vacation" or "out of office" responses should not be returned for this mail, e.g. to prevent vacation notices from being sent to all other subscribers of a mailing list. uses this header to affect prioritization of queued email, with "Precedence: special-delivery" messages delivered sooner. With modern high-bandwidth networks delivery priority is less of an issue than it once was. respects a fine-grained automatic response suppression mechanism, the X-Auto-Response-Suppress header.Microsoft, Auto Response Suppress, 2010, microsoft reference, 2010 Sep 22
  • References: of the message that this is a reply to, and the message-id of the message the previous reply was a reply to, etc.
  • Reply-To: Address that should be used to reply to the message.
  • Sender: Address of the actual sender acting on behalf of the author listed in the From: field (secretary, list manager, etc.).
  • Archived-At: A direct link to the archived form of an individual email message.

Note that the To: field is not necessarily related to the addresses to which the message is delivered. The actual delivery list is supplied separately to the transport protocol, , which may or may not originally have been extracted from the header content. The "To:" field is similar to the addressing at the top of a conventional letter which is delivered according to the address on the outer envelope. In the same way, the "From:" field does not have to be the real sender of the email message. Some mail servers apply systems to messages being relayed. Data pertaining to server's activity is also part of the header, as defined below.

SMTP defines the trace information of a message, which is also saved in the header using the following two fields:

  • Received: when an SMTP server accepts a message it inserts this trace record at the top of the header (last to first).
  • Return-Path: when the delivery SMTP server makes the final delivery of a message, it inserts this field at the top of the header.

Other header fields that are added on top of the header by the receiving server may be called trace fields, in a broader sense.

  • Authentication-Results: when a server carries out authentication checks, it can save the results in this field for consumption by downstream agents.This extensible field is defined by RFC 7001, that also defines an registry of Email Authentication Parameters.
  • Received-SPF: stores results of checks in more detail than Authentication-Results.RFC 7208.
  • Auto-Submitted: is used to mark automatically generated messages.Defined in RFC 3834, and updated by RFC 5436.
  • VBR-Info: claims whitelistingRFC 5518.

Message body

Content encoding
Email was originally designed for 7-bit . ξ1 Most email software is but must assume it will communicate with 7-bit servers and mail readers. The standard introduced character set specifiers and two content transfer encodings to enable transmission of non-ASCII data: for mostly 7 bit content with a few characters outside that range and for arbitrary binary data. The and extensions were introduced to allow transmission of mail without the need for these encodings, but many still do not support them fully. In some countries, several encoding schemes coexist; as the result, by default, the message in a non-Latin alphabet language appears in non-readable form (the only exception is coincidence, when the sender and receiver use the same encoding scheme). Therefore, for international , is growing in popularity.

Plain text and HTML
Most modern graphic allow the use of either or for the message body at the option of the user. messages often include an automatically generated plain text copy as well, for compatibility reasons.

Advantages of HTML include the ability to include in-line links and images, set apart previous messages in , wrap naturally on any display, use emphasis such as and , and change styles. Disadvantages include the increased size of the email, privacy concerns about , abuse of HTML email as a vector for attacks and the spread of .

Some web based recommend that all posts be made in plain-text, with 72 or 80 for all the above reasons, but also because they have a significant number of readers using such as .

Some allow rich formatting using their proprietry (RTF), but this should be avoided unless the recipient is guaranteed to have a compatible .

Servers and client applications
Messages are exchanged between hosts using the with software programs called (MTAs); and delivered to a mail store by programs called (MDAs, also sometimes called local delivery agents, LDAs). Users can retrieve their messages from servers using standard protocols such as or , or, as is more likely in a large environment, with a protocol specific to , or . Webmail interfaces allow users to access their mail with any standard , from any computer, rather than relying on an email client. Programs used by users for retrieving, reading, and managing email are called (MUAs).

Mail can be stored on the , on the side, or in both places. Standard formats for mailboxes include and . Several prominent email clients use their own proprietary format and require conversion software to transfer email between them. Server-side storage is often in a proprietary format but since access is through a standard protocol such as , moving email from one server to another can be done with any supporting the protocol.

Accepting a message obliges an MTA to deliver it,In practice, some accepted messages may nowadays not be delivered to the recipient's InBox, but instead to a Spam or Junk folder which, especially in a corporate environment, may be inaccessible to the recipient and when a message cannot be delivered, that MTA must send a back to the sender, indicating the problem.

Filename extensions
Upon reception of email messages, applications save messages in operating system files in the file system. Some clients save individual messages as separate files, while others use various database formats, often proprietary, for collective storage. A historical standard of storage is the format. The specific format used is often indicated by special :
Used by many email clients including , , , , , and Postbox. The files are in format, containing the email header as well as the message contents and attachments in one or more of several formats.
Used by .
Used by and .
Used by , , and based on the format.

Some applications (like ) leave attachments encoded in messages for searching while also saving separate copies of the attachments. Others separate attachments from messages and save them in a specific directory.

Mobile devices, such as and , commonly have the ability to receive email. Since users may always have their mobile device with them, users may access email significantly faster on these devices than through other methods, such as or .

URI scheme mailto
The , as registered with the , defines the mailto: scheme for SMTP email addresses. Though its use is not strictly defined, URLs of this form are intended to be used to open the new message window of the user's mail client when the URL is activated, with the address as defined by the URL in the To: field.RFC 2368 section 3 : by Paul Hoffman in 1998 discusses operation of the "mailto" URL.


Web-based email
Many email providers have a web-based email client (e.g. , , and ). This allows users to log into the email account by using any compatible to send and receive their email. Mail is typically not downloaded to the client, so can't be read without a current Internet connection.

POP3 email services
The 3 (POP3) is a mail access protocol used by a client application to read messages from the mail server. Received messages are often deleted from the . POP supports simple download-and-delete requirements for access to remote mailboxes (termed maildrop in the POP RFC's).

IMAP email servers
The (IMAP) provides features to manage a mailbox from multiple devices. Small portable devices like are increasingly used to check email while travelling, and to make brief replies, larger devices with better keyboard access being used to reply at greater length. IMAP shows the headers of messages, the sender and the subject and the device needs to request to download specific messages. Usually mail is left in folders in the mail server.

MAPI email servers
(MAPI) is a messaging architecture and an API based on the Component Object Model (COM) for Microsoft Windows.


occurs when a person sends a message with angry or antagonistic content. The term is derived from the use of the word Incendiary to describe particularly heated email discussions. Flaming is assumed to be more common today because of the ease and impersonality of email communications: confrontations in person or via telephone require direct interaction, where social norms encourage civility, whereas typing a message to another person is an indirect interaction, so civility may be forgotten.

Email bankruptcy
Also known as "email fatigue", email bankruptcy is when a user ignores a large number of email messages after falling behind in reading and answering them. The reason for falling behind is often due to information overload and a general sense there is so much information that it is not possible to read it all. As a solution, people occasionally send a boilerplate message explaining that the email inbox is being cleared out. law professor is credited with coining this term, but he may only have popularized it.

In business
Email was widely accepted by the business community as the first broad electronic communication medium and was the first 'e-revolution' in business communication. Email is very simple to understand and like postal mail, email solves two basic problems of communication: logistics and synchronization (see below).

Email also solves minor problems with communication that exist with methods such as postal mail and telephone communication. For instance, sending an email is less expensive than sending postal mail, and it is much faster. Using email eliminates the problem of trying to get a hold of someone that is common with telephone communication and it is also more practical than postal mail because it does not require paper that can be lost or damaged.

LAN based email is also an emerging form of usage for business. It not only allows the business user to download mail when offline, it also allows the small business user to have multiple users' email IDs with just one email connection.

  • The problem of logistics: Much of the business world relies on communications between people who are not physically in the same building, area, or even country; setting up and attending an in-person meeting, , or can be inconvenient, time-consuming, and costly. Email provides a method of exchanging information between two or more people with no set-up costs and that is generally far less expensive than a physical meeting or phone call.
  • The problem of synchronisation: With communication by meetings or phone calls, participants must work on the same schedule, and each participant must spend the same amount of time in the meeting or call. Email allows : each participant may control their schedule independently.

Most business workers today spend from one to two hours of their working day using email: reading, ordering, sorting, 're-contextualizing' fragmented information, and writing email. The use of email is increasing worldwide:
  • Information overload: Email is a – the sender controls who receives the information. Convenient availability of and use of "copy all" can lead to people receiving unwanted or irrelevant information of no use to them.
  • Inconsistency: Email can duplicate information. This can be a problem when a large team is working on documents and information while not in constant contact with the other members of their team.

Despite these disadvantages, email has become the most widely used medium of communication within the business world. A 2010 study on workplace communication by Paytronics found 83% of U.S. knowledge workers felt email was critical to their success and productivity at work.By Om Malik, GigaOm. " Is Email a Curse or a Boon?" September 22, 2010. Retrieved October 11, 2010.

Research on email marketing
Marketing research suggests that opt-in email marketing can be viewed as useful by consumers if it contains information such as special sales offerings and new product information. Offering interesting hyperlinks or generic information on consumer trends is less useful. This research by Martin et al. (2003) also shows that if consumers find email marketing useful, they are likely to visit a store, thereby overcoming limitations of Internet marketing such as not being able to touch or try on a product.

Email has become widely used on smart phones. Mobile apps for email increase accessibility to the medium. While before users could only access email on computers, it is now possible for users to check their email out of the home and out of the library while on the go. Alerts can also be sent to the phone to notify them immediately of new messages. This has given email the ability to be used for more frequent communication between users and allowed them to check their email and write messages throughout the day. Today, there are an estimated 1.4 billion email users worldwide and 50 billion non-spam emails that are sent daily.

It was found that US adults check their email more than they browse the web or check their accounts, making email the most popular activity for users to do on their smart phones. 78% of the respondents in the study revealed that they check their email on their phone. Matt McGee. March 28, 2013. Email Is Top Activity On Smartphones, Ahead Of Web Browsing & Facebook (Study) It was also found that 30% of consumers use only their smartphone to check their email, and 91% were likely to check their email at least once per day on their smartphone. However, the percentage of consumers using email on smartphone ranges and differs dramatically across different countries. For example, in comparison to 75% of those consumers in the US who used it, only 17% in India did. Jordan van Rijn. April 2014. The ultimate mobile email statistics overview


Attachment size limitation
Email messages may have one or more attachments, i.e. MIME parts intended to provide copies of files. Attachments serve the purpose of delivering binary or text files of unspecified size. In principle there is no technical intrinsic restriction in the , protocol or limiting the size or number of attachments. In practice, however, email service providers implement various limitations on the permissible size of files or the size of an entire message.

Furthermore, due to technical reasons, often a small attachment can increase in size when sent, which can be confusing to senders when trying to assess whether they can or cannot send a file by email, and this can result in their message being rejected.

As larger and larger file sizes are being created and traded, many users are either forced to upload and download their files using an , or more popularly, use online file sharing facilities or services, usually over web-friendly , in order to send and receive them.

Information overload
A December 2007 blog post described information overload as "a $650 Billion Drag on the Economy", and the New York Times reported in April 2008 that "E-MAIL has become the bane of some people's professional lives" due to information overload, yet "none of the current wave of high-profile Internet start-ups focused on email really eliminates the problem of email overload because none helps us prepare replies". GigaOm posted a similar article in September 2010, highlighting research that found 57% of knowledge workers were overwhelmed by the volume of email they received. Technology investors reflect similar concerns.

In October 2010, CNN published an article titled "Happy Information Overload Day" that compiled research about email overload from IT companies and productivity experts. According to Basex, the average knowledge worker receives 93 messages per day. Subsequent studies have reported higher numbers. Marsha Egan, an email productivity expert, called email technology both a blessing and a curse in the article. She stated, "Everyone just learns that they have to have it dinging and flashing and open just in case the boss e-mails," she said. "The best gift any group can give each other is to never use e-mail urgently. If you need it within three hours, pick up the phone."

Spamming and computer viruses
The usefulness of email is being threatened by four phenomena: , , , and .

Spamming is unsolicited commercial (or bulk) email. Because of the minuscule cost of sending email, spammers can send hundreds of millions of email messages each day over an inexpensive Internet connection. Hundreds of active spammers sending this volume of mail results in for many computer users who receive voluminous unsolicited email each day.Rich Kawanagh. The top ten email spam list of 2005. ITVibe news, 2006, January 02, ITvibe.comHow Microsoft is losing the war on spam

Email worms use email as a way of replicating themselves into vulnerable computers. Although the affected computers, the problem is most common today on the operating system.

The combination of spam and worm programs results in users receiving a constant drizzle of junk email, which reduces the usefulness of email as a practical tool.

A number of mitigate the impact of spam. In the , has also passed a law, the , attempting to regulate such email. also has very strict spam laws restricting the sending of spam from an Australian ISP,Spam Bill 2003 ( PDF) but its impact has been minimal since most spam comes from regimes that seem reluctant to regulate the sending of spam.

Email spoofing
occurs when the email message header is designed to make the message appear to come from a known or trusted source. and methods typically use spoofing to mislead the recipient about the true message origin.

Email bombing
is the intentional sending of large volumes of messages to a target address. The overloading of the target email address can render it unusable and can even cause the mail server to crash.

Privacy concerns
Today it can be important to distinguish between Internet and internal email systems. Internet email may travel and be stored on networks and computers without the sender's or the recipient's control. During the transit time it is possible that third parties read or even modify the content. Internal mail systems, in which the information never leaves the organizational network, may be more secure, although personnel and others whose function may involve monitoring or managing may be accessing the email of other employees.

Email privacy, without some security precautions, can be compromised because:

  • email messages are generally not encrypted.
  • email messages have to go through intermediate computers before reaching their destination, meaning it is relatively easy for others to intercept and read messages.
  • many Internet Service Providers (ISP) store copies of email messages on their mail servers before they are delivered. The backups of these can remain for up to several months on their server, despite deletion from the mailbox.
  • the "Received:"-fields and other information in the email can often identify the sender, preventing anonymous communication.

There are applications that can serve as a remedy to one or more of the above. For example, or the can be used to encrypt traffic from the user machine to a safer network while , , SMEmail, SMEmail – A New Protocol for the Secure E-mail in Mobile Environments, Proceedings of the Australian Telecommunications Networks and Applications Conference (ATNAC'08), pp. 39–44, Adelaide, Australia, Dec. 2008. or can be used for message encryption, and SMTP STARTTLS or SMTP over /Secure Sockets Layer can be used to encrypt communications for a single mail hop between the SMTP client and the SMTP server.

Additionally, many do not protect logins and passwords, making them easy to intercept by an attacker. Encrypted authentication schemes such as prevent this.

Finally, attached files share many of the same hazards as those found in . Attached files may contain or .

Tracking of sent mail
The original SMTP mail service provides limited mechanisms for tracking a transmitted message, and none for verifying that it has been delivered or read. It requires that each mail server must either deliver it onward or return a failure notice (bounce message), but both software bugs and system failures can cause messages to be lost. To remedy this, the introduced (delivery receipts) and (return receipts); however, these are not universally deployed in production. (A complete Message Tracking mechanism was also defined, but it never gained traction; see RFCs 3885RFC 3885, SMTP Service Extension for Message Tracking through 3888.RFC 3888, Message Tracking Model and Requirements)

Many ISPs now deliberately disable non-delivery reports (NDRs) and delivery receipts due to the activities of spammers:

  • Delivery Reports can be used to verify whether an address exists and so is available to be spammed
  • If the spammer uses a forged sender email address (), then the innocent email address that was used can be flooded with NDRs from the many invalid email addresses the spammer may have attempted to mail. These NDRs then constitute spam from the ISP to the innocent user

In the absence of standard methods, a range of system based around the use of have been developed. However, these are often seen as underhand or raising privacy concerns, and only work with e-mail clients that support rendering of HTML. Many mail clients now default to not showing "web content". "Outlook: Web Bugs & Blocked HTML Images", providors can also disrupt web bugs by pre-caching images. "Gmail blows up e-mail marketing...", Ron Amadeo, Dec 13 2013, Ars Technica

U.S. government
The U.S. state and federal governments have been involved in electronic messaging and the development of email in several different ways.

Starting in 1977, the U.S. Postal Service (USPS) recognized that electronic messaging and electronic transactions posed a significant threat to First Class mail volumes and revenue. The USPS explored an electronic messaging initiative in 1977 and later disbanded it. Twenty years later, in 1997, when email volume overtook postal mail volume, the USPS was again urged to embrace email, and the USPS declined to provide email as a service. The USPS initiated an experimental email service known as . E-COM provided a method for the simple exchange of text messages. In 2011, shortly after the USPS reported its state of financial bankruptcy, the USPS Office of Inspector General (OIG) began exploring the possibilities of generating revenue through email servicing. Electronic messages were transmitted to a post office, printed out, and delivered as hard copy. To take advantage of the service, an individual had to transmit at least 200 messages. The delivery time of the messages was the same as First Class mail and cost 26 cents. Both the and the opposed E-COM. The FCC concluded that E-COM constituted common carriage under its jurisdiction and the USPS would have to file a .In re Request for declaratory ruling and investigation by Graphnet Systems, Inc., concerning the proposed E-COM service, FCC Docket No. 79-6 (September 4, 1979) Three years after initiating the service, USPS canceled E-COM and attempted to sell it off. History of the United States Postal Service, USPS, 13 November 2014Hardy, Ian R; The Evolution of ARPANET Email; 1996-05-13; History Thesis Paper; University of California at BerkeleyJames Bovard, The Law Dinosaur: The US Postal Service, CATO Policy Analysis (February 1985)

The early ARPANET dealt with multiple email clients that had various, and at times incompatible, formats. For example, in the , the "@" sign meant "kill line" and anything before the "@" sign was ignored, so Multics users had to use a command-line option to specify the destination system. The desired to have uniformity and interoperability for email and therefore funded efforts to drive towards unified inter-operable standards. This led to David Crocker, John Vittal, Kenneth Pogran, and publishing RFC 733, "Standard for the Format of ARPA Network Text Message" (November 21, 1977), a subset of which provided a stable base for common use on the ARPANET, but which was not fully effective, and in 1979, a meeting was held at BBN to resolve incompatibility issues. recounted the meeting in RFC 808, "Summary of Computer Mail Services Meeting Held at BBN on 10 January 1979" (March 1, 1982), which includes an appendix listing the varying email systems at the time. This, in turn, led to the release of David Crocker's RFC 822, "Standard for the Format of ARPA Internet Text Messages" (August 13, 1982). RFC 822 is a small adaptation of RFC 733's details, notably enhancing the portion, to use , that were being developed at the same time.

The took over operations of the ARPANET and Internet from the Department of Defense, and initiated , a new for the network. A part of the NSFNet AUP forbade commercial traffic. In 1988, arranged for an interconnection of with NSFNET on an experimental basis. The following year email interconnected with NSFNET. Within a few years the commercial traffic restriction was removed from NSFNETs AUP, and NSFNET was privatised.

In the late 1990s, the grew concerned with fraud transpiring in email, and initiated a series of procedures on spam, fraud, and phishing. Cybertelecom : SPAM Reference In 2004, FTC jurisdiction over spam was codified into law in the form of the Several other U.S. federal agencies have also exercised jurisdiction including the and the .

NASA has provided email capabilities to astronauts aboard the Space Shuttle and International Space Station since 1991 when a was used aboard mission to send the first email via . ξ2 Today astronauts aboard the International Space Station have email capabilities via the throughout the station and are connected to the ground at 10 Earth to station and 3 Mbit/s station to Earth, comparable to home connection speeds.

See also

Further reading
  • Cemil Betanov, Introduction to X.400, Artech House, ISBN 0-89006-597-7.
  • Marsha Egan, " Inbox Detox and The Habit of Email Excellence", Acanthus Publishing ISBN 978-0-9815589-8-1
  • Lawrence Hughes, Internet e-mail Protocols, Standards and Implementation, Artech House Publishers, ISBN 0-89006-939-5.
  • Kevin Johnson, Internet Email Protocols: A Developer's Guide, Addison-Wesley Professional, ISBN 0-201-43288-9.
  • Pete Loshin, Essential Email Standards: RFCs and Protocols Made Practical, John Wiley & Sons, ISBN 0-471-34597-0.
  • Sara Radicati, Electronic Mail: An Introduction to the X.400 Message Handling Standards, Mcgraw-Hill, ISBN 0-07-051104-7.
  • John Rhoton, Programmer's Guide to Internet Mail: SMTP, POP, IMAP, and LDAP, Elsevier, ISBN 1-55558-212-5.
  • John Rhoton, X.400 and SMTP: Battle of the E-mail Protocols, Elsevier, ISBN 1-55558-165-X.
  • David Wood, Programming Internet Mail, O'Reilly, ISBN 1-56592-479-7.

External links

    ^ (2024). 9780596002978, .
    ^ (2024). 9781593270100, No Starch Press.

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