Email

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Electronic mail ( email or e-mail ) is a method of exchanging messages ("mail") between people using electronic devices. The first email entry usage was limited to the 1960s and in the mid-1970s has taken the form now known as email. Email operates across the network of computers, which today mainly are the Internet. Some early email systems require authors and recipients to both online at the same time, similar to instant messaging. The current email system is based on the store-and-forward model. The mail server receives, forwards, sends and saves messages. Neither their users nor their computers are required to be online simultaneously; they only need to connect briefly, usually to an email server or webmail interface, as long as it takes to send or receive messages.

Originally an ASCII text communication medium only, Internet emails were extended by Multipurpose Internet Mail Extensions (MIME) to carry text in another set of characters and attachments of multimedia content. International mail, with international email addresses using UTF-8, has been standardized, but by 2017 it has not been widely adopted.

The history of modern Internet email services reaches back to the early ARPANET, with a standard for encoding email messages published in early 1973 (RFC 561). Email messages sent in the early 1970s are very similar to the basic emails sent today. Email has an important role in creating the Internet, and the conversion of ARPANET to the Internet in the early 1980s generates the core of today's services.

Video Email

Terminology

Historically, the term electronic mail is used generally for the transmission of any electronic document. For example, some writers in the early 1970s used the term to describe the transmission of fax documents. As a result, it is difficult to find the first quote for the use of the term with the more specific meaning it has today.

The e-mail is most commonly referred to as email or e-mail since about 1993, but spelling variations have been used:

email is the most common form that is used online, and is required by IETF Request for Comments (RFC) and workgroups and increasingly by style guides. The spelling also appears in most dictionaries.
e-mail is a format that sometimes appears in English and English edited English, published as reflected in the Corpus of Contemporary American English data, but is not preferred in some style guides.
mail is the form used in the original protocol standard, RFC 524 . This service is referred to as mail , and one part of the e-mail is called .
EMail is a traditional form that has been used in the RFC for "Author Address" and is explicitly requested "for historical reasons".
E-mail is sometimes used, the initial capitalization of E as in the same abbreviation as E-piano , E- guitar , A-bomb , and H-bomb .

Internet e-mail consists of envelopes and content; The content in turn consists of headers and entities.

Maps Email

Origin

Computer-based letters and messages became possible with the advent of time-sharing computers in the early 1960s, and informal methods of using shared files to convey messages were soon extended to the first email system. Most early mainframe developers and minicomputers develop similar mail applications, but are generally incompatible. Over time, gateway networks and complicated routing systems connect many of them. Many US universities are part of the ARPANET (created in the late 1960s), aimed at the portability of the software among its systems. Portability that helps make Simple Mail Transfer Protocol (SMTP) increasingly influential.

For a time in the late 1980s and early 1990s, it seemed likely that either the exclusive commercial system or the X.400 email system, part of the Government Open Systems Interconnection Profile (GOSIP), would dominate. However, after the last restriction to bring commercial traffic over the Internet expired in 1995, the combination of factors made the current Internet sequence of the standard SMTP, POP3 and IMAP email protocols.

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Operation

The diagram on the right shows the sequence of events that occur when Alice's sender transmits messages using an email user agent (MUA) addressed to the recipient's email address.

The MUA format the message in email format and uses the sending protocol, the profile of the Simple Mail Transfer Protocol (SMTP), to send message content to a local mail delivery agent (MSA), in this case smtp.a. org .
The MSA specifies the destination address provided in the SMTP protocol (not from the message headers), in this case bob@b.org . The section before the @ sign is the local part of the address, often the recipient's username, and the part after the @ sign is the domain name. The MSA resolves the domain name to determine the fully qualified domain name of the mail server in the Domain Name System (DNS).
The DNS server for the b.org domain ( ns.b.org ) responds with any MX record that lists the mail exchange server for that domain, in which case < i> mx.b.org , the message transfer server (MTA) run by the receiving ISP.
smtp.a.org sends messages to mx.b.org using SMTP. This server may need to forward the message to another MTA before the message reaches the final message delivery agent (MDA).
MDA sends it to user mailbox bob .
MUA Budi takes messages using Post Office Protocol (POP3) or Internet Message Access Protocol (IMAP).

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

Alice or Bob can use clients connected to a corporate email system, such as IBM Lotus Notes or Microsoft Exchange. These systems often have their own internal email format and their clients typically communicate with email servers using vendor-specific protocols. The server sends or receives email through the Internet through the Internet email gateway of the product which also performs the necessary reformatting. If Alice and Bob work in the same company, all transactions can take place entirely within one corporate email system.
Alice may not have an MUA on her computer but may be connected to a webmail service.
Alice's computer can run its own MTA, so avoid transfer in step 1.
Bob can retrieve his email in various ways, such as logging in to mx.b.org and reading it directly, or by using a webmail service.
Domains usually have multiple mail exchange servers so they can continue to receive emails even if the primary ones are not available.

Many MTAs are used to receive messages for recipients on the Internet and do their best to deliver them. Such MTAs are called open mail relays . This is very important in the early days of the Internet when network connections were unreliable. However, this mechanism is proven to be exploited by unsolicited bulk email generators and as a result open letter relay becomes scarce, and many MTAs do not receive messages from open mail relays.

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Message format

The format of Internet email messages is now determined by RFC 5322, with non-ASCII data encoding and attachment of multimedia content defined in RFC 2045 through RFC 2049, collectively referred to as Multipurpose Internet Mail Extension or MIME RFC 5322 replaced RFC 2822 earlier in 2008, and in turn RFC 2822 in 2001 replaced RFC 822 - which has been the standard for Internet email for nearly 20 years. Published in 1982, RFC 822 is based on previous RFC 733 for ARPANET.

Internet email messages consist of two main sections, message headers and message body, which are collectively known as content. Headers are structured into fields such as From, Ke, CC, Subject, Date, and other information about email. In the process of sending email messages between systems, SMTP communicates delivery parameters and information using message header columns. The body contains messages, as unstructured text, sometimes containing a signature block at the end. The header is separated from the body by a blank line.

Message header

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

Informally, each line of text in the header beginning with a printable character starts a separate field. The field name starts on the first character of the line and ends before the ":" separator character. The separator is then followed by the field value ("body" field). The value is passed to the next line if the line has a space or tab as their first character. Field names and values â€‹â€‹are restricted to 7-bit ASCII characters. Some non-ASCII values â€‹â€‹can be represented using words that are MIME encoded.

Header field

The email header field can be multi-row, and each row must be at most 78 characters and no more than 998 characters. The header field defined by RFC 5322 can only contain US-ASCII characters; for character encoding in another set, the syntax specified in RFC 2047 can be used. Recently the IETF EAI workgroup has set some standard line extensions, replacing previous experimental extensions, to allow UTF-8 encoded Unicode characters to be used in headers. Specifically, this allows the email address to use non-ASCII characters. The address is supported by Google and Microsoft products, and promoted by multiple governments.

The message header must include at least the following fields:

From : Email address, and optionally author name (s). In many email clients can not be changed except through changing account settings.
Date : The local time and date when the message was written. Like the From: field, many email clients auto-complete this when sending. The receiving client can then display the time in their local time format and time zone.

RFC 3864 describes the registration procedure for message header fields in IANA; it provides permanent and temporary field names, including fields defined for MIME, netnews, and HTTP, and relevant RFC references. Common header fields for email include:

Go : The email address (es), and optionally the message recipient name. Shows the main recipient (some allowed), for secondary recipients see Cc: and Bcc: below.
Subject : A brief summary of the message topic. Certain abbreviations are commonly used in the subject, including "RE:" and "FW:".
Cc : Copies of carbon; Many email clients will mark emails in someone'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 are not usually registered in the message headers.)
Content-Type: Information about how messages are displayed, usually MIME types.
Presence : usually with "bulk", "trash", or "list" values; used to indicate that "vacation" or "offsite" answers automatically may not be returned for this email, e.g. to prevent holiday notifications from being sent to all other customers of the mailing list. Sendmail uses this field to influence prioritizing queued emails, with a message of "Presentation: custom delivery" being sent faster. With modern high-bandwidth networks, priority delivery is less of a problem than ever before. Microsoft Exchange appreciates the fine auto response suppression mechanism, the X-Auto-Response-Suppress field.
Message ID : Also a field created automatically; used to prevent dual delivery and for reference in In-Reply-To: (see below).
In-Reply-To : Message-ID of the message that this is the reply. Used to connect shared messages together. This field applies only to reply messages.
References : The message-ID of the message that this is a reply to, and the message-id of the previous reply message is a reply, etc.
Reply-To : The address that should be used to reply to a message.
Submitter : The actual sender address acting on behalf of the author listed in the From field: (secretary, list manager, etc.).
Archived-On : Direct link to the archived form of individual email messages.

Note that the To: field is not always related to the destination address of the message delivery. The actual sending list is provided separately to the transport protocol, SMTP, which may or may not initially be extracted from the header content. The "To:" field is similar to the address at the top of a conventional letter that is sent according to the address on the outer envelope. In the same way, the "From:" field does not have to be the actual sender of the email message. Some email servers implement email authentication systems to relayed messages. Data relating to server activity is also a part of the header, as defined below.

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

Received : when the SMTP server receives the message, it inserts this track record at the top of the header (last to first).
Path-Back : when the SMTP delivery server makes final delivery of a message, this will enter this field at the top of the header.

Any other fields added above the header by the receiving server can be called the field trace , in a broader sense.

Result-Authentication : when the server performs authentication checks, it can store results in this field for consumption by downstream agents.
Received-SPF : keeps the SPF check results in more detail than the Authentication Results.
Automatically Delivered : used to automatically mark messages created.
VBR-Info : claim VBR whitelist

Message content

Content encoding

Internet email was originally designed for 7-bit ASCII. Most of the 8-bit net email software but should assume it will communicate with 7-bit servers and email readers. The MIME standard introduces a character set of specifiers and two encoded content transfers to allow for transmitted non-ASCII: quoted data to be printed for most 7-bit content with some characters outside that range and base64 for arbitrary binary data. The 8BITMIME and BINARY extensions were introduced to allow mail delivery without the need for this encoding, but many mail transport agencies still do not fully support them. In some countries, some coding schemes co-exist; as a result, by default, messages in non-Latin alphabetical languages â€‹â€‹appear in unreadable form (the only exception is chance, when the sender and receiver use the same encoding scheme). Therefore, for the international character set, Unicode is growing in popularity.

Plain text and HTML

Most modern graphics email clients allow the use of plain text or HTML for the message body in user options. HTML email messages often include automatically generated text copies automatically, for compatibility reasons. Excess HTML includes the ability to include in-line links and images, organize previous messages in quotation marks, wrap naturally on every view, using presses like underline and italics, and change font styles. Disadvantages include increased email size, privacy concerns about web bugs, abuse of HTML email as vectors for phishing attacks and malicious software deployment.

Some web-based mailing lists recommend that all posts are made in plain text, with 72 or 80 characters per line for all of the above reasons, but also because they have a large number of readers that use text-based email clients like Mutt. Some Microsoft email clients allow rich formatting using their proprietary Rich Text Format (RTF), but this should be avoided unless the recipient is guaranteed to have a compatible email client.

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Server and client applications

Messages are exchanged between hosts using the Simple Mail Transfer Protocol with a software program called a mail-transfer agent (MTA); and sent to the mail shop by a program called an email delivery agent (MDAs, also sometimes called local delivery agent, LDA). Receiving a message requires the MTA to send it, and when the message can not be sent, the MTA must send a bounce message back to the sender, indicating the problem.

Users can retrieve their messages from the server using standard protocols such as POP or IMAP, or, as is more likely in large enterprise environments, with protocols specific to Novell Groupwise, Lotus Notes or Microsoft Exchange Server. Programs used by users to retrieve, read, and manage emails are called email user agents (MUA).

Mail can be stored on the client, on the server side, or in both places. Standard formats for mailboxes include Maildir and mbox. Some leading email clients use their own proprietary formats and require conversion software to transfer mail between them. Server-side storage is often in proprietary format, but because access through standard protocols like IMAP, moving mail from one server to another can be done with any MUA that supports the protocol.

Many email users do not currently run MTA, MDA or MUA programs themselves, but use a web-based email platform, such as Gmail, Hotmail, or Yahoo! Mail, which does the same task. Such webmail interfaces allow users to access their email with any standard web browser, from any computer, rather than relying on email clients.

File name extensions

After receiving an email message, the client's email application stores messages in the operating system file in the file system. Some clients store individual messages as separate files, while others use a variety of database formats, often patented, for collective storage. The historical storage standard is the mbox format. The specific format used is often indicated by a custom filename extension:

eml: Used by many email clients including Novell GroupWise, Microsoft Outlook Express, Lotus records, Windows Mail, Mozilla Thunderbird, and Postbox. The files contain email content as plain text in MIME format, containing headers and body of emails, including attachments in one or more of several formats.
emlx: Used by Apple Mail.
msg: Used by Microsoft Office Outlook and OfficeLogic Groupware.
mbx: Used by Opera Mail, KMail, and Apple Mail based on mbox format.

Some apps (such as Apple Mail) leave attachments encoded in messages for search while also storing separate copies of attachments. Others separate attachments from messages and store them in specific directories.

mailto URI scheme

The URI scheme, as registered with IANA, defines the mailto: scheme for SMTP email addresses. Although their use is not strictly defined, the URL of this form is intended to be used to open a new message window from the user's mail client when the URL is enabled, with the address specified by the URL in the To: field.

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Type

Web-based email

Many email providers have web-based mail clients (eg AOL Mail, Gmail, Outlook.com, Hotmail, and Yahoo! Mail). It allows users to login to an email account using a compatible web browser to send and receive their email. Mail is usually not downloaded to clients, so it can not be read without an Internet connection at this time.

POP3 email service

Post Office Protocol 3 (POP3) is an email access protocol used by a client application to read messages from an email server. Messages received are often deleted from the server. POP supports a simple download-and-delete requirement for access to the remote mailbox (called maildrop in POP RFC).

IMAP email server

The Internet Message Access Protocol (IMAP) provides features for managing mailboxes from multiple devices. Small portable devices such as smartphones are increasingly being used to check email on the go, and to make quick replies, larger devices with better keyboard access are used to reply longer. IMAP displays message headers, senders, and subjects and the device needs to request to download certain messages. Usually the mail is left in the folder on the mail server.

MAPI email server

The Messaging Application Programming Interface (MAPI) is used by Microsoft Outlook to communicate with Microsoft Exchange Server - and various other mail server products such as Axigen Mail Server, Kerio Connect, Scalix, Zimbra, HP OpenMail, IBM Lotus Notes, Zarafa and Bynari where vendors adding MAPI support to enable their products to be accessed directly through Outlook.

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Usage

Business and organizational use

Email has been widely accepted by businesses, governments and non-governmental organizations in the developed world, and this is one of the most important pieces of 'e-revolution' in workplace communication (with other keyboards being widespread adoption of high-speed Internet). A sponsored 2010 study of workplace communication found that 83% of US knowledge workers feel email is critical to their success and productivity in the workplace.

It has several key benefits for businesses and other organizations, including:

Facilitate logistics: Most of the business world relies on communication between people who are not physically in the same building, area, or even country; organizing and attending live meetings, phone calls, or conference calls can be uncomfortable, time consuming, and expensive. Email provides a method of exchanging information between two or more people without set-up fees and it is generally much cheaper than physical encounters or phone calls.
Help with sync: With real-time communication through meetings or phone calls, participants must work on the same schedule, and each participant must spend the same amount of time in a meeting or call. Email allows asynchrony: each participant can control their schedule independently.
Reduce cost: Sending email is much cheaper than sending postal mail, or long distance phone calls, telex or telegram.
Increase speed: Much faster than most alternatives.
Create a "written" note: Unlike in-phone or in-person conversations, email by nature creates detailed written records of communication, the identity of the sender and recipient, as well as the date and time of message delivery. In the event of a contractual or legal dispute, stored emails may be used to prove that an individual is notified of a particular problem, because each email has a date and time recorded on it.

Email marketing

Email marketing through "opt-in" is often used successfully to send special sales offers and new product information. Depending on the recipient's culture, unauthorized emails - such as "opt-in" - are likely to be considered unwanted "spam emails".

Personal use

Personal computer

Many users access their personal emails from friends and family members using personal computers in their homes or apartments.

Mobile

Email has been used on smartphones and across all types of computers. The mobile "app" for email increases accessibility to the media for users outside their homes. While in the early years of email, users can only access email on desktop computers, by 2010, it is possible for users to check their email when they are away from home, whether they are in the city or around the world. Signs can also be sent to a smartphone or other device to immediately notify them of new messages. It has emailed the ability to be used for more frequent communication between users and allows them to check their email and write messages throughout the day. As of 2011, there are about 1.4 billion email users worldwide and 50 billion non-spam emails sent every day.

Individuals often check email on the smartphone for both private and work-related messages. It's found that US adults check their emails more than they browse the web or check their Facebook accounts, making email the most popular activity for users to do on their smartphones. 78% of respondents in the study revealed that they were checking their emails on their phones. It was also found that 30% of consumers only use their smartphones to check their email, and 91% will likely check their emails at least once per day on their smartphones. However, the percentage of consumers using email on smartphones ranges dramatically differed in different countries. For example, compared to 75% of US consumers who use it, only 17% in India are using it.

Reduced usage among youth

In 2010, the number of Americans who visited email websites had dropped 6 percent after reaching a peak in November 2009. For people 12 to 17, the number fell by 18 percent. Young people prefer instant messaging, texting and social media, and email is not designed for them. Technology writer Matt Richtel said in The New York Times that emails are like VCRs, phonograph records and movie cameras - no longer cool and something a parent does.

The 2015 survey of Android users shows that 13 to 24 people use the messaging app 3.5 times more than those over 45, and much less using email.

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Problem

Attachment size limit

Email messages may have one or more attachments, which are additional files added to email. Common attachments include Microsoft Word documents, pdf documents and scanned paper document images. In principle there is no technical limit on the size or number of attachments, but in practice, email clients, servers and Internet service providers impose limits on file size, or full email - typically up to 25 MB or less. Additionally, due to technical reasons, the attachment size as seen by this transport system may differ from what the user sees, which can confuse the sender while trying to judge whether they can safely send files via email. Where larger files need to be shared, file hosting services of all sorts are available; and generally recommended. Some large files, such as digital photos, color presentations, and video or music files are too large for some email systems.

Information overload

The email state for knowledge workers and "white-collar" employees has caused concern that recipients face "excessive information" in handling increased email volumes. With growth on mobile devices, by default employees may also receive work-related emails outside their business day. This can lead to increased stress, decreased satisfaction with employment, and some observers even argue that it can have significant negative economic effects, as attempts to read multiple emails can reduce productivity.

Spam

"Spam" email is the term used to describe unsolicited bulk email. The low cost of sending such emails means that up to 2003 to 30% of total email traffic has become spam. and threatening the use of email as a practical tool. The 2003 US CAN-SPAM Act and similar laws elsewhere have some impact, and a number of effective anti-spam techniques now largely reduce the impact of spam by filtering or denying it to most users, but the volume submitted is still very high- -and increasingly no ads for the product, but malicious content or links.

Malware

Different types of malicious emails exist. These range from various types of email fraud, including "social engineering" scams such as "Nigerian mail" down payment, to phishing, bombardment emails and email worms.

Email spoofing

Email spoofing occurs when email message headers are designed to make messages appear to come from known or trusted sources. Spam emails and phishing methods usually use spoofing to mislead the recipient about the origin of the actual message. Email spoofing can be done as a joke, or as part of a criminal attempt to trick someone or an organization. An example of potentially deceptive email spoofing is if someone creates an email that appears to be an invoice from a large company, and then sends it to one or more recipients. In some cases, these fraudulent emails incorporate recognized organizational logos and even email addresses may seem legitimate.

Email bombing

Email bombing is a deliberate delivery of a large volume of messages to the target address. The advantages of the target email address can make it unusable and can even cause the mail server to crash.

Privacy issues

Today it can be important to distinguish between internet and internal mail system. Internet emails can travel and be stored on networks and computers without the sender or receiver control. During transit time, there is the possibility of third parties reading or even modifying the content. The internal mail system, where information never leaves the organization's network, may be safer, although information technology personnel and others whose function may involve monitoring or management may access other employee emails.

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

email messages are generally not encrypted.
email messages must go through an intermediate computer before reaching their destination, which means it's relatively easy for others to intercept and read messages.
Many Internet service providers (ISPs) keep copies of email messages on their mail servers before they are sent. These backups may remain for several months on their servers, even if they are removed from the mailbox.
"Accepted:" - fields and other information in an email can often identify the sender, preventing anonymous communications.
an invisible web bug embedded in email content can alert the sender of an email whenever an email is read, or re-read, and from which IP address. It can also reveal whether email is read on a smartphone or PC, or Apple Mac device via a user-agent string.

There is a cryptographic application that can serve as a cure for one or more of the above. For example, a Virtual Private Network or Tor anonymity network can be used to encrypt traffic from a user's machine to a more secure network while GPG, PGP, SMEmail, or S/MIME can be used for end-to-end message encryption, and SMTP STARTTLS or SMTP via the Transport Security Layer/Secure Sockets Layer can be used to encrypt communications for one letter hop between SMTP clients and SMTP servers.

In addition, many email user agents do not protect logins and passwords, making them easily tapped by attackers. Encrypted authentication schemes like SASL prevent this. Finally, the attached file shares many of the same dangers as found in peer-to-peer file sharing. The attached file may contain trojan or virus.

Flaming

Flaming happens when someone sends a message (or many messages) with angry or antagonistic content. The term is derived from the use of the word "burner" to describe heated email discussions. The ease and inappropriateness of email communications mean that social norms that encourage personal courtesy or by phone are absent and decency can be forgotten.

Email bankruptcy

Also known as "email fatigue", email bankruptcy is when users ignore large numbers of email messages after falling behind in reading and answering them. The reason for falling behind is often because of information overload and general understanding there is so much information that it is impossible to read everything. As a solution, people sometimes send a "boilerplate" message that explains that their email inbox is full, and that they are in the process of clearing all messages. Harvard Law Law professor Lawrence Lessig is credited with this term, but he may only popularize it.

Internationalization

Originally the internet email was actually ASCII text based. MIME now allows body content text and some text header content in international character sets, but headers and other email addresses use UTF-8, while standards have not been widely adopted.

Tracking of sent mail

The original SMTP mail service provides a limited mechanism for tracking messages sent, and no one verifies that messages have been sent or read. It is required that each mail server must send it or return a notification of failure (bounce message), but either software bugs or system failures may cause the message to disappear. To address this, the IETF introduces Delivery Status Notices (delivery receipts) and Message Disposal Notices (return receipts); However, this is not universally deployed in production. (Full Messaging Tracking Mechanism is also defined, but never gets any appeal: see RFC 3885 to 3888.)

Many ISPs now deliberately disable undelivered reports (NDRs) and delivery receipts due to spammers activity:

The Delivery report can be used to verify if an address exists and if so, it indicates to the spammer that it is available for spammed.
If the spammer uses a spoofing email address, then the innocent email address used may be flooded with NDRs from the many invalid email addresses the spam sender may want to send. This NDR is then a spam of ISPs to innocent users.

In the absence of standard methods, various systems based around the use of web bugs have been developed. However, this is often seen as a crude action or raising privacy concerns, and only works with email clients that support HTML rendering. Many email clients now do not display "web content". Email providers can also interfere with web bugs with pre-cached images.