Electronic mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email was thus conceived as the electronic (

digital Digital usually refers to something using discrete digits, often binary digits. Technology and computing Hardware *Digital electronics, electronic circuits which operate using digital signals ** Digital camera, which captures and stores digital ...

) version of, or counterpart to,

mail The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal sys ...

, at a time when "mail" meant only physical mail (hence '' e- + mail''). Email later became a ubiquitous (very widely used) communication medium, to the point that in current use, an email address is often treated as a basic and necessary part of many processes in business, commerce, government, education, entertainment, and other spheres of daily life in most countries. ''Email'' is the medium, and each message sent therewith is also called an ''email.'' The term is a

mass noun In linguistics, a mass noun, uncountable noun, non-count noun, uncount noun, or just uncountable, is a noun with the syntactic property that any quantity of it is treated as an undifferentiated unit, rather than as something with discrete elemen ...

. Email operates across

computer network A computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are ...

s, primarily the

Internet The Internet (or internet) is the global system of interconnected computer networks that uses the Internet protocol suite (TCP/IP) to communicate between networks and devices. It is a '' network of networks'' that consists of private, p ...

, and also

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, school, laboratory, university campus or office building. By contrast, a wide area network (WAN) not only covers a large ...

s. Today's email systems are based on a store-and-forward model. Email servers accept, forward, deliver, and store messages. Neither the users nor their computers are required to be online simultaneously; they need to connect, typically to a

mail server Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX ho ...

or a

webmail Webmail (or web-based email) is an email service that can be accessed using a standard web browser. It contrasts with email service accessible through a specialised email client software. Examples of webmail providers are 1&1 Ionos, AOL Mail, ...

interface to send or receive messages or download it. Originally an

ASCII ASCII ( ), abbreviated from American Standard Code for Information Interchange, is a character encoding standard for electronic communication. ASCII codes represent text in computers, telecommunications equipment, and other devices. Because ...

text-only communications medium, Internet email was extended by

Multipurpose Internet Mail Extensions Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs. Messag ...

(MIME) to carry text in other character sets and multimedia content attachments.

International email International email arises from the combined provision of ''internationalized domain names'' (IDN) and ''email address internationalization'' (EAI).Started with: The result is email that contains international characters (characters which do not e ...

, with internationalized email addresses using

UTF-8 UTF-8 is a variable-length character encoding used for electronic communication. Defined by the Unicode Standard, the name is derived from ''Unicode'' (or ''Universal Coded Character Set'') ''Transformation Format 8-bit''. UTF-8 is capable of e ...

, is standardized but not widely adopted.

Terminology

The term ''electronic mail'' has been in use with its modern meaning since 1975, and variations of the shorter ''E-mail'' have been in use since 1979: * ''email'' is now the common form, and recommended by

style guide A style guide or manual of style is a set of standards for the writing, formatting, and design of documents. It is often called a style sheet, although that term also has multiple other meanings. The standards can be applied either for gene ...

s. It is the form required by

IETF The Internet Engineering Task Force (IETF) is a standards organization for the Internet and is responsible for the technical standards that make up the Internet protocol suite (TCP/IP). It has no formal membership roster or requirements an ...

Requests for Comments (RFC) and working groups. 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'' is the form favored in edited published American English and British English writing as reflected in the Corpus of Contemporary American English data, but is falling out of favor in some style guides. * ''E-mail'' is sometimes used. The original usage in June 1979 occurred in the journal ''

Electronics The field of electronics is a branch of physics and electrical engineering that deals with the emission, behaviour and effects of electrons using electronic devices. Electronics uses active devices to control electron flow by amplification ...

'' in reference to the

United States Postal Service The United States Postal Service (USPS), also known as the Post Office, U.S. Mail, or Postal Service, is an independent agency of the executive branch of the United States federal government responsible for providing postal service in the ...

initiative called

E-COM E-COM, short for Electronic Computer Originated Mail, was a hybrid mail process used from 1982 to 1985 by the U.S. Postal Service (USPS) to print electronically originated mail, and deliver it in envelopes to customers within two days of transmis ...

, which was developed in the late 1970s and operated in the early 1980s. * ''Email'' is also used. * ''EMAIL'' was used by

CompuServe CompuServe (CompuServe Information Service, also known by its initialism CIS) was an American online service provider, the first major commercial one in the world – described in 1994 as "the oldest of the Big Three information services (the oth ...

starting in April 1981, which popularized the term. * ''EMail'' is a traditional form used in RFCs for the "Author's Address". The service is often simply referred to as ''mail'', and a single piece of electronic mail is called a ''message''. The conventions for fields within emails — the “To,” “From,” “CC,” “BCC” etc. — began with RFC-680 in 1975. An Internet email consists of an ''envelope'' and ''content''; the content consists of a ''header'' and a ''body''.

History

Computer-based messaging between users of the same system became possible after the advent of

time-sharing In computing, time-sharing is the sharing of a computing resource among many users at the same time by means of multiprogramming and multi-tasking.DEC Timesharing (1965), by Peter Clark, The DEC Professional, Volume 1, Number 1 Its emergence ...

in the early 1960s, with a notable implementation by MIT's CTSS project in 1965. Most developers of early

mainframe A mainframe computer, informally called a mainframe or big iron, is a computer used primarily by large organizations for critical applications like bulk data processing for tasks such as censuses, industry and consumer statistics, enterprise ...

s and

minicomputer A minicomputer, or colloquially mini, is a class of smaller general purpose computers that developed in the mid-1960s and sold at a much lower price than mainframe and mid-size computers from IBM and its direct competitors. In a 1970 survey, ' ...

s developed similar, but generally incompatible, mail applications. In 1971 the first

ARPANET The Advanced Research Projects Agency Network (ARPANET) was the first wide-area packet-switched network with distributed control and one of the first networks to implement the TCP/IP protocol suite. Both technologies became the technical fou ...

network mail was sent, introducing the now-familiar address syntax with the '@' symbol designating the user's system address. Over a series of RFCs, conventions were refined for sending mail messages over the

File Transfer Protocol The File Transfer Protocol (FTP) is a standard communication protocol used for the transfer of computer files from a server to a client on a computer network. FTP is built on a client–server model architecture using separate control and da ...

. Proprietary electronic mail systems soon began to emerge. IBM,

and

Xerox Xerox Holdings Corporation (; also known simply as Xerox) is an American corporation that sells print and digital document products and services in more than 160 countries. Xerox is headquartered in Norwalk, Connecticut (having moved from St ...

used in-house mail systems in the 1970s; CompuServe sold a commercial intraoffice mail product from 1978 and IBM and Xerox from 1981.; ; ; ; DEC's ALL-IN-1 and Hewlett-Packard's HPMAIL (later HP DeskManager) were released in 1982; development work on the former began in the late 1970s and the latter became the world’s largest selling email system. The Simple Mail Transfer Protocol (SMTP) protocol was implemented on the ARPANET in 1983.

LAN Lan or LAN may also refer to: Science and technology * Local asymptotic normality, a fundamental property of regular models in statistics * Longitude of the ascending node, one of the orbital elements used to specify the orbit of an object in spa ...

email systems emerged in the mid 1980s. For a time in the late 1980s and early 1990s, it seemed likely that either a proprietary commercial system or the

X.400 X.400 is a suite of ITU-T Recommendations that defines the ITU-T Message Handling System (MHS). At one time, the designers of X.400 were expecting it to be the predominant form of email, but this role has been taken by the SMTP-based Internet e- ...

email system, part of the

Government Open Systems Interconnection Profile The Government Open Systems Interconnection Profile (GOSIP) was a specification that profiled open networking products for procurement by governments in the late 1980s and early 1990s. Timeline * 1988 - GOSIP: Government Open Systems Interconnectio ...

(GOSIP), would predominate. However, once the final restrictions on carrying commercial traffic over the Internet ended in 1995, a combination of factors made the current Internet suite of SMTP,

POP3 In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common ...

and

IMAP In computing, the Internet Message Access Protocol (IMAP) is an Internet standard protocol used by email clients to retrieve email messages from a mail server over a TCP/IP connection. IMAP is defined by . IMAP was designed with the goal of per ...

email protocols the standard (see

Protocol Wars A long-running debate in computer science known as the Protocol Wars occurred from the 1970s to the 1990s when engineers, organizations and nations became polarized over the issue of which communication protocol would result in the best and most ...

Operation

The following is a typical sequence of events that takes place when sender

Alice Alice may refer to: * Alice (name), most often a feminine given name, but also used as a surname Literature * Alice (''Alice's Adventures in Wonderland''), a character in books by Lewis Carroll * ''Alice'' series, children's and teen books by ...

transmits a message using a

mail user agent The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...

(MUA) addressed to the

email address An email address identifies an email box to which messages are delivered. While early messaging systems used a variety of formats for addressing, today, email addresses follow a set of specific rules originally standardized by the Internet Engineer ...

of the recipient. email

# The MUA formats the message in email format and uses the submission protocol, a profile of the Simple Mail Transfer Protocol (SMTP), to send the message content to the local

mail submission agent A message submission agent (MSA), or mail submission agent, is a computer program or software agent that receives electronic mail messages from a mail user agent (MUA) and cooperates with a mail transfer agent (MTA) for delivery of the mail. It us ...

(MSA), in this case ''smtp.a.org''. # The MSA determines the destination address provided in the SMTP protocol (not from the message header) — in this case, ''[email protected]'' — which is a fully qualified domain address (FQDA). The part before the @ sign is the ''local part'' of the address, often the username of the recipient, and the part after the @ sign is a

domain name A domain name is a string that identifies a realm of administrative autonomy, authority or control within the Internet. Domain names are often used to identify services provided through the Internet, such as websites, email services and more. As ...

. The MSA resolves a domain name to determine the fully qualified domain name of the

in the

Domain Name System The Domain Name System (DNS) is a hierarchical and distributed naming system for computers, services, and other resources in the Internet or other Internet Protocol (IP) networks. It associates various information with domain names assigned t ...

(DNS). # The DNS server for the domain ''b.org'' (''ns.b.org'') responds with any MX records listing the mail exchange servers for that domain, in this case ''mx.b.org'', a message transfer agent (MTA) server run by the recipient's ISP. # smtp.a.org sends the message to mx.b.org using SMTP. This server may need to forward the message to other MTAs before the message reaches the final

message delivery agent A message delivery agent (MDA), or mail delivery agent, is a computer software component that is responsible for the delivery of e-mail messages to a local recipient's mailbox., ''Internet Mail Architecture'', D. Crocker (July 2009) It is also ca ...

(MDA). # The MDA delivers it to the mailbox of user ''bob''. # Bob's MUA picks up the message using either the

Post Office Protocol In computing, the Post Office Protocol (POP) is an application-layer Internet standard protocol used by e-mail clients to retrieve e-mail from a mail server. POP version 3 (POP3) is the version in common use, and along with IMAP the most common ...

(POP3) or the Internet Message Access Protocol (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 IBM Lotus Notes or

Microsoft Microsoft Corporation is an American multinational technology corporation producing computer software, consumer electronics, personal computers, and related services headquartered at the Microsoft Redmond campus located in Redmond, Washi ...

Exchange. 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 an 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 mx.b.org 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 '' open mail relays''. 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 unsolicited bulk email and as a consequence open mail relays have become rare, and many MTAs do not accept messages from open mail relays.

Message format

The basic Internet message format used for email is defined by , with encoding of non-ASCII data and multimedia content attachments defined in RFC 2045 through RFC 2049, collectively called ''

'' or ''MIME''. The extensions in

apply only to email. RFC 5322 replaced the earlier RFC 2822 in 2008, then RFC 2822 in 2001 replaced RFC 822 – the standard for Internet email for decades. Published in 1982, RFC 822 was based on the earlier RFC 733 for the ARPANET. Internet email messages consist of two sections, "header" and "body". These are known as "content". The header is structured into fields such as From, To, CC, Subject, Date, and other information about the email. In the process of transporting email messages between systems, SMTP communicates delivery parameters and information using message header fields. The body contains the message, as unstructured text, sometimes containing a

signature block A signature block (often abbreviated as signature, sig block, sig file, .sig, dot sig, siggy, or just sig) is a personalized block of text automatically appended at the bottom of an email message, Usenet article, or forum post. Email and Usenet ...

at the end. The header is separated from the body by a blank line.

Message header

RFC 5322 specifies the

syntax In linguistics, syntax () is the study of how words and morphemes combine to form larger units such as phrases and sentences. Central concerns of syntax include word order, grammatical relations, hierarchical sentence structure ( constituenc ...

of the email header. Each email message has a header (the "header section" of the message, according to the specification), comprising a number of fields ("header fields"). Each field has a name ("field name" or "header field name"), followed by the separator character ":", and a value ("field body" or "header field body"). Each field name begins in the first character of a new line in the header section, and begins with a non- whitespace

printable character In ISO/IEC 646 (commonly known as ASCII) and related standards including ISO 8859 and Unicode, a graphic character is any character intended to be written, printed, or otherwise displayed in a form that can be read by humans. In other words, it i ...

. It ends with the separator character ":". The separator is followed by the field value (the "field body"). The value can continue onto subsequent lines if those lines have space or tab as their first character. Field names and, without SMTPUTF8, field bodies are restricted to 7-bit ASCII characters. Some non-ASCII values may be represented using MIME encoded words.

Header fields

Email header fields can be multi-line, with each line recommended to be no more than 78 characters, although the limit is 998 characters. Header fields defined by RFC 5322 contain only US-ASCII characters; for encoding characters in other sets, a syntax specified in RFC 2047 may be used. In some examples, the IETF EAI working group defines some standards track extensions, replacing previous experimental extensions so

encoded

Unicode Unicode, formally The Unicode Standard,The formal version reference is is an information technology standard for the consistent encoding, representation, and handling of text expressed in most of the world's writing systems. The standard, ...

characters may be used within the header. In particular, this allows email addresses to use non-ASCII characters. Such addresses are supported by Google and Microsoft products, and promoted by some government agents. The message header must include at least the following fields: * ''From'': The email address, and, optionally, the name of the author(s). Some email clients are changeable through account settings. * ''Date'': The local time and date the message was written. Like the ''From:'' field, many email clients fill this in automatically before sending. The recipient's client may display the time in the format and time zone local to them. RFC 3864 describes registration procedures for message header fields at the

IANA The Internet Assigned Numbers Authority (IANA) is a standards organization that oversees global IP address allocation, autonomous system number allocation, root zone management in the Domain Name System (DNS), media types, and other Interne ...

; it provides fo
permanent
an

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. Certain abbreviations are commonly used in the subject, including "RE:" and "FW:". * ''Cc'':

Carbon copy Before the development of photographic copiers, a carbon copy was the under-copy of a typed or written document placed over carbon paper and the under-copy sheet itself (not to be confused with the carbon print family of photographic reproduc ...

; Many email clients mark email in one's inbox differently depending on whether they are in the To: or Cc: list. * ''Bcc'': Blind carbon copy; addresses are usually only specified during SMTP delivery, and not usually listed in the message header. *

Content-Type A media type (also known as a MIME type) is a two-part identifier for file formats and format contents transmitted on the Internet. The Internet Assigned Numbers Authority (IANA) is the official authority for the standardization and publication o ...

: Information about how the message is to be displayed, usually a

MIME Multipurpose Internet Mail Extensions (MIME) is an Internet standard that extends the format of email messages to support text in character sets other than ASCII, as well as attachments of audio, video, images, and application programs. Message ...

type. * ''Precedence'': commonly with values "bulk", "junk", or "list"; used to indicate automated "vacation" or "out of office" responses should not be returned for this mail, e.g. to prevent vacation notices from sent to all other subscribers of a mailing list.

Sendmail Sendmail is a general purpose internetwork email routing facility that supports many kinds of mail-transfer and delivery methods, including the Simple Mail Transfer Protocol (SMTP) used for email transport over the Internet. A descendant of the ...

uses this field 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 was. Microsoft Exchange respects a fine-grained automatic response suppression mechanism, the ''X-Auto-Response-Suppress'' field. * '' Message-ID'': Also an automatic-generated field to prevent multiple deliveries and for reference in In-Reply-To: (see below). * ''In-Reply-To'': Message-ID of the message this is a reply to. Used to link related messages together. This field only applies to reply messages. * ''References'': Message-ID of the message this is a reply to, and the message-id of the message the previous reply was a reply to, etc. * ': Address should be used to reply to the message. * ''Sender'': Address of the 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. The ''To:'' field may be unrelated to the addresses to which the message is delivered. The delivery list is supplied separately to the transport protocol,

SMTP The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients ty ...

, which may be extracted from the header content. The "To:" field is similar to the addressing at the top of a conventional letter delivered according to the address on the outer envelope. In the same way, the "From:" field may not be the sender. Some mail servers apply email authentication systems to messages relayed. Data pertaining to the server's activity is also part of the header, as defined below. SMTP defines the ''trace information'' of a message saved in the header using the following two fields: * ''Received'': after an SMTP server accepts a message, it inserts this trace record at the top of the header (last to first). * ''Return-Path'': after the delivery SMTP server makes the ''final delivery'' of a message, it inserts this field at the top of the header. Other fields added on top of the header by the receiving server may be called ''trace fields''. * ''Authentication-Results'': after a server verifies authentication, it can save the results in this field for consumption by downstream agents. * ''Received-SPF'': stores results of SPF checks in more detail than Authentication-Results. * ''DKIM-Signature'': stores results of DomainKeys Identified Mail (DKIM) decryption to verify the message was not changed after it was sent. * ''Auto-Submitted'': is used to mark automatic-generated messages. * ''VBR-Info'': claims VBR whitelisting

Message body

Content encoding

Internet email was designed for 7-bit ASCII. Most email software is 8-bit clean, 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: quoted printable for mostly 7-bit content with a few characters outside that range and base64 for arbitrary binary data. The

8BITMIME The Simple Mail Transfer Protocol (SMTP) is an Internet standard communication protocol for electronic mail transmission. Mail servers and other message transfer agents use SMTP to send and receive mail messages. User-level email clients typi ...

and BINARY extensions were introduced to allow transmission of mail without the need for these encodings, but many

mail transport agent Within the Internet email system, a message transfer agent (MTA), or mail transfer agent, or mail relay is software that transfers electronic mail messages from one computer to another using SMTP. The terms mail server, mail exchanger, and MX host ...

s may not support them. In some countries, e-mail software violates by sending rawNot using Internationalized Email or MIME non-ASCII text and several encoding schemes co-exist; as a result, by default, the message in a non-Latin alphabet language appears in non-readable form (the only exception is a coincidence if the sender and receiver use the same encoding scheme). Therefore, for international

character set Character encoding is the process of assigning numbers to graphical characters, especially the written characters of human language, allowing them to be stored, transmitted, and transformed using digital computers. The numerical values tha ...

is growing in popularity.

Plain text and HTML

Most modern graphic

email client An email client, email reader or, more formally, message user agent (MUA) or mail user agent is a computer program used to access and manage a user's email. A web application which provides message management, composition, and reception functio ...

s allow the use of either

plain text In computing, plain text is a loose term for data (e.g. file contents) that represent only characters of readable material but not its graphical representation nor other objects (floating-point numbers, images, etc.). It may also include a limit ...

HTML The HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It can be assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaS ...

for the message body at the option of the user.

HTML email HTML email is the use of a subset of HTML to provide formatting and semantic markup capabilities in email that are not available with plain text: Text can be linked without displaying a URL, or breaking long URLs into multiple pieces. Text ...

messages often include an automatic-generated plain text copy for compatibility. Advantages of HTML include the ability to include in-line links and images, set apart previous messages in block quotes, wrap naturally on any display, use emphasis such as underlines and

italics In typography, italic type is a cursive font based on a stylised form of calligraphic handwriting. Owing to the influence from calligraphy, italics normally slant slightly to the right. Italics are a way to emphasise key points in a printed t ...

, and change

font In metal typesetting, a font is a particular size, weight and style of a typeface. Each font is a matched set of type, with a piece (a " sort") for each glyph. A typeface consists of a range of such fonts that shared an overall design. In mo ...

styles. Disadvantages include the increased size of the email, privacy concerns about web bugs, abuse of HTML email as a vector for

phishing Phishing is a type of social engineering where an attacker sends a fraudulent (e.g., spoofed, fake, or otherwise deceptive) message designed to trick a person into revealing sensitive information to the attacker or to deploy malicious softwa ...

attacks and the spread of malicious software. Some e-mail clients interpret the body as HTML even in the absence of a Content-Type: html header field; this may cause various problems. Some web-based

mailing list A mailing list is a collection of names and addresses used by an individual or an organization to send material to multiple recipients. The term is often extended to include the people subscribed to such a list, so the group of subscribers is re ...

s recommend all posts be made in plain text, with 72 or 80 characters per line for all the above reasons, and because they have a significant number of readers using text-based email clients such as Mutt. Various informal conventions evolved for marking up plain text in email and

usenet Usenet () is a worldwide distributed discussion system available on computers. It was developed from the general-purpose Unix-to-Unix Copy (UUCP) dial-up network architecture. Tom Truscott and Jim Ellis conceived the idea in 1979, and it wa ...

posts, which later led to the development of formal languages like

setext Setext (Structure Enhanced Text) is a lightweight markup language used to format plain text documents such as e-newsletters, Usenet postings, and e-mails. In contrast to some other markup languages (such as HTML), the markup is easily readable ...

''(c. 1992)'' and

many others Many may refer to: * grammatically plural in number *an English quantifier used with count nouns indicating a large but indefinite number of; at any rate, more than a few ;Place names * Many, Moselle, a commune of the Moselle department in Franc ...

, the most popular of them being markdown. Some

email clients may allow rich formatting using their proprietary

Rich Text Format ) As an example, the following RTF code would be rendered as follows: This is some bold text. Character encoding A standard RTF file can only consist of 7-bit ASCII characters, but can use escape sequences to encode other characters. T ...

(RTF), but this should be avoided unless the recipient is guaranteed to have a compatible email client.

Servers and client applications

Messages are exchanged between hosts using the Simple Mail Transfer Protocol with software programs called

mail transfer agent The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...

s (MTAs); and delivered to a mail store by programs called mail delivery agents (MDAs, also sometimes called local delivery agents, LDAs). Accepting a message obliges an MTA to deliver it, and when a message cannot be delivered, that MTA must send a bounce message back to the sender, indicating the problem. Users can retrieve their messages from servers using standard protocols such as

POP Pop or POP may refer to: Arts, entertainment, and media Music * Pop music, a musical genre Artists * POP, a Japanese idol group now known as Gang Parade * Pop!, a UK pop group * Pop! featuring Angie Hart, an Australian band Albums * ''Pop'' ( ...

, or, as is more likely in a large

corporate A corporation is an organization—usually a group of people or a company—authorized by the state to act as a single entity (a legal entity recognized by private and public law "born out of statute"; a legal person in legal context) and r ...

environment, with a

proprietary {{Short pages monitor {{DEFAULTSORT:Email Internet terminology

Mail The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal sys ...

History of the Internet Computer-related introductions in 1971