Process Essay On E-Mail
Email, or electronic mail, is the most common method of exchanging digital messages and remains one of the most popular services currently available via the Internet, with over 90% of US Internet users actively using email. Here you’ll find an overview of the modern email system and infrastructure, as well as its origin and use.
For a shorter, less technical overview, please see Are You Confused By The Technicalities?
The Email System
Email systems consist of computer servers that process and store messages on behalf of users who connect to the email infrastructure via an email client or web interface.
When someone sends an email, the message is transferred from his or her computer to the server associated with the recipient’s address, usually via a number of other servers.
In more detail (please refer to the illustration on the right):
- A user (Alice) sends an email message and connects to an SMTP (Simple Mail Transfer Protocol) server as configured in her email client or Mail User Agent (MUA).
- On the SMTP server, a Mail Transfer Agent (MTA) looks at the recipient address and looks up the domain part of the address to determine its destination.
- After querying a Domain Name System (DNS) server for the name of the Mail eXchanger (MX) for the recipient’s domain name…
- …the SMTP server will send the message to that server via the SMTPprotocol.
- The receiving server will store the message and make it available to the recipient (Bob), who can access it via web, POP, or IMAP.
Email was actually invented before the Internet itself, and was a crucial tool in the development of an interoperable computer network. Email is believed to have originated at MIT (Massachusetts Institute of Technology) in 1965 to allow users of a local time-sharing mainframe computer to communicate with each other.
This quickly evolved to systems that could communicate with other, compatible systems, and from 1969 the ARPANET computer network of the United States Department of Defense experimented with inter-system email transfers using the now familiar “@” sign to separate usernames from machine names. From the early 1980s networked personal computers on Local Area Networks also started supporting simple email systems.
When ARPANET later evolved into what we now know as the Internet, email was already the standard method of communication.
Email servers are responsible for receiving, storing, forwarding, and delivering messages to and from email users. Messages are exchanged between servers using the SMTP protocol with various MTAs (Mail Transfer Agents) such as Sendmail, Postfix, qmail, or Exim. Messages can be stored on the server for the user to access, they can be downloaded and stored in the email client for offline use, or stored both places.
When an email server accepts a message it is obliged to deliver it, or otherwise return a delivery failure message to the sender. This ensures that an email message cannot disappear into thin air and implies that the sender of an email can trust the integrity of the email system.
Occasionally a message can be neither delivered nor returned, usually as a result of a spam message to a non-existent recipient from a falsified sender address (see Anti-spam Info for more information).
There are 3 main types of email servers:
- SMTP servers: A Simple Mail Transfer Protocol server can refer to either a physical computer or a Mail Transfer Agent (MTA), which is a software program running on the machine. The MTA receives and delivers messages to and from other email servers, and from email users (also known as “relaying”).
- POP servers: A Post Office Protocol server is a piece of software that gives an email user access to the email stored in the user’s account on that server. The user can download the messages using a MUA (email client) and store the email locally for later viewing.
- IMAP servers: An Internet Message Access Protocol server is a software program running on a server that provides full access to all the folders the user has created on the server. The email user can synchronize all the folders and messages on the server with the data stored locally using a MUA with IMAP capabilities.
A user can access the email messages stored on an email server using an email client or Mail User Agent (MUA) such as Outlook, Thunderbird, and Eudora.
The MUA connects to the email server via POP to download messages from a folder, or the more advanced IMAP protocol to synchronize all messages in the folders that exist on the server. When the user sends a message, the client connects to the server using the SMTP protocol.
A Webmail interface is a web-based email service that is accessible in a web browser such as Internet Explorer or Firefox. Most email services offer web interfaces to the email stored on the server.
So-called webmail services are often faster because they access the stored data more directly via a web browser without the user having to download a piece of software that has to be set up and configured locally.
The enormous popularity of email has induced a large number of email services offering various types and levels of email functionality and related services.
Although most ISPs (Internet Service Providers) include simple email services with their accounts, many people prefer dedicated email services that provide more storage space, more functionality, other integrated communication services, etc.
The free service segment is dominated by companies such as Google and Microsoft that make money from advertisers who pay to expose the email users to advertisements. GMail, for instance, shows so-called contextual advertisements that relate to the actual content of the message being displayed. This has raised privacy concerns among some users, although many users instead focus on the benefits such as large storage space and user-friendliness.
Subscription-based services often provide more dedicated email services as they depend on customer loyalty to support their existence. Typically they offer more professional services with more advanced functionality, integrated with email and web hosting services, and they are usually ad-free. Paid services often provide better customer support as they are required to be more dependable than the free alternatives.
The Email Message
The actual email message contains text and characters that represent delivery information and content, and must adhere to certain standards defined by IETF (The Internet Engineering Task Force) to ensure that it can be properly handled by the various computer systems that will process it.
An email message consists of two main sections: The header and the body.
The header can be thought of as the email equivalent of a regular envelope, and is structured into fields (lines) containing information about the sender, receiver, subject, date, etc of the message. It also includes one entry for each server that has processed the message on its way from sender to recipient, which is very useful for tracking its origin — especially if the message looks suspicious (for instance in phishing attempts).
In Runbox Webmail you can click the “View full headers” icon to the top right in the message view mode to view all the headers of a message.
More information: IANA’s (The Internet Assigned Numbers Authority) full list of possible message headers.
The message body constitutes the content of the message, and can include several parts and attachments in many different formats.
In the early days email only contained plain text in ASCII format, but as email usage has evolved it has become necessary to support both HTML and other types of content. Today, email messages are usually encoded with the MIME (Multipurpose Internet Mail Extensions) standard that allows email to support text in various character sets, attached files, multimedia content, etc.
Since such messages can contain both information and small pieces of software not apparent to the user, care should be taken by the recipient when opening HTML messages or attachments in a client — or use Webmail which is more secure as possible malicious software in the message can’t easily be run on the local computer.
To view the entire email message source you can click the “View source” icon to the top right in the message view mode.
In modern society people increasingly use email and other forms of digital communication to create and maintain social networks. Especially in academic institutions and in the business world, email was embraced early on as an effective means of asyncrhonous communication — somewhere in between the telephone and regular mail.
With the enormous increase in the number of email messages sent and received worldwide in recent years, it has become increasingly important to employ filters that can sort out legitimate email and user-friendly interfaces that simplify the task of processing messages.
Email Abuse and Spam
Because email is an extremely cost-effective means of communication that allows a user to send large amounts of messages to a great number of recipients, it has become a very popular tool for spreading information and software programs that are unsolicited and/or malicious.
There are several challenges that both email administrators and email users should be aware of:
Spamming is the act of sending unsolicited commercial (or bulk) email, often to large numbers of recipients. Today it is very inexpensive to send millions of email messages, and only a few positive responses to an email advertisement can make spamming worthwhile to the individuals that send spam.
Runbox includes several powerful spam and virus filters to protect our users from unsolicited or potentially harmful messages, such as SpamAssassin, Dspam, and Clam AntiVirus.
See our anti-spam section for information on how to avoid spam.
In recent years spammers have increasingly banded with malicious software makers, creating so-called email worms that infect vulnerable computers through email, multiply, and spread to other computers (often using contacts from the infected system’s address book), causing a constant barrage of junk email.
It is always advisable to use updated anti-virus software on your computer to avoid being infected.
See our anti-virus section for information on how to avoid worms and viruses.
Email spoofing is a technique to alter the header information of an email to make the message appear to come from a known or trusted source. Spoofing is often used in so-called phishing where individuals attempt to collect personal information in order to access bank accounts or other sensitive services.
Because the SMTP protocol was created in a time when email abuse was not yet conceived, it is fairly easy to falsify the content of a message and equally difficult to verify its origin. Several efforts are being made to standardize the verification of email messages such that sources of criminal email activity can be uncovered.
We hope this article has contributed to understanding what email is and how it works. If you have any questions about email, feel free to ask in the Runbox Forum or use the Support Center.
This article is about the communications medium. For the former manufacturing conglomerate, see Email Limited.
"Inbox" redirects here. For the Google product, see Inbox by Gmail.
Electronic Mail (email or e-mail) is a method of exchanging messages ("mail") between people using electronic devices. Email first entered limited use in the 1960s and by the mid-1970s had taken the form now recognized as email. Email operates across computer networks, which today is primarily the Internet. Some early email systems required the author and the recipient to both be online at the same time, in common with instant messaging. 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 only briefly, typically to a mail server or a webmail interface, for as long as it takes to send or receive messages.
Originally an ASCII text-only communications medium, Internet email was extended by Multipurpose Internet Mail Extensions (MIME) to carry text in other character sets and multimedia content attachments. International email, with internationalized email addresses using UTF-8, has been standardized, but as of 2017 it has not been widely adopted.
The history of modern Internet email services reaches back to the early ARPANET, with standards for encoding email messages published as early as 1973 (RFC 561). An email message sent in the early 1970s looks very similar to a basic email sent today. Email had an important role in creating the Internet, and the conversion from ARPANET to the Internet in the early 1980s produced the core of the current services.
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 fax document transmission. 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.
Electronic mail has been most commonly called email or e-mail since around 1993, but variations of the spelling have been used:
- email is the most common form used online, and is required by IETFRequests for Comments (RFC) and working groups and increasingly by style guides. This spelling also appears in most dictionaries.
- e-mail is the format that sometimes appears 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.
- mail was the form used in the original protocol standard, RFC 524. 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 E-piano, E-guitar, A-bomb, and H-bomb.
An Internet e-mail consists of an envelope and content; the content in turn consists of a header and a body.
Main article: History of email
Computer-based mail and messaging became possible with the advent of time-sharing computers in the early 1960s, and informal methods of using shared files to pass messages were soon expanded into the first mail systems. Most developers of early mainframes and minicomputers developed similar, but generally incompatible, mail applications. Over time, a complex web of gateways and routing systems linked many of them. Many US universities were part of the ARPANET (created in the late-1960s), which aimed at software portability between its systems. That portability helped make the Simple Mail Transfer Protocol (SMTP) increasingly influential.
For a time in the late 1980s and early 1990s, it seemed likely that either a proprietary commercial system or the X.400 email system, part of the Government Open Systems Interconnection Profile (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 and IMAP email protocols the standard.
The diagram to the right shows a typical sequence of events that takes place when sender Alice transmits a message using a mail user agent (MUA) addressed to the email address of the recipient.
- 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 (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 firstname.lastname@example.org. 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. The MSA resolves a domain name to determine the fully qualified domain name of the mail server in the Domain Name System (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 (MDA).
- The MDA delivers it to the mailbox of user bob.
- Bob's MUA picks up the message using either the Post Office Protocol (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 IBMLotus Notes or MicrosoftExchange. 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 webmail 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 Internet email message format is now defined by RFC 5322, with encoding of non-ASCII data and multimedia content attachments being defined in RFC 2045 through RFC 2049, collectively called Multipurpose Internet Mail Extensions 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 ARPANET.
Internet email messages consist of two major sections, the message header and the message body, collectively 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 at the end. The header is separated from the body by a blank line.
Each message has exactly one header, which is structured into fields. 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 printable character 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 ASCII characters. Some non-ASCII values may be represented using MIME encoded words.
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 US-ASCII 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 UTF-8 encoded Unicode characters to 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 governments.
The message header must include at least the following fields:
- From: The email address, 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.
RFC 3864 describes registration procedures for message header fields at the IANA; it provides for permanent and provisional 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; Many email clients will 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: Information about how the message is to be displayed, usually a MIME 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. Sendmail 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 once was. Microsoft Exchange respects a fine-grained automatic response suppression mechanism, the X-Auto-Response-Suppress field.
- Message-ID: Also an automatically generated field; used to prevent multiple delivery and for reference in In-Reply-To: (see below).
- In-Reply-To: Message-ID of the message that this is a reply to. Used to link related messages together. This field only applies for reply messages.
- References: Message-ID 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, SMTP, 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 email authentication 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 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.
- Received-SPF: stores results of SPF checks in more detail than Authentication-Results.
- Auto-Submitted: is used to mark automatically generated messages.
- VBR-Info: claims VBR whitelisting
Internet email was originally 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 MIME 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 and BINARY extensions were introduced to allow transmission of mail without the need for these encodings, but many mail transport agents 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 character sets, Unicode is growing in popularity.
Plain text and HTML
Most modern graphic email clients allow the use of either plain text or HTML for the message body at the option of the user. HTML email 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 block quotes, wrap naturally on any display, use emphasis such as underlines and italics, and change font styles. Disadvantages include the increased size of the email, privacy concerns about web bugs, abuse of HTML email as a vector for phishing attacks and the spread of malicious software.
Some web-based mailing lists recommend that all posts be made in plain-text, with 72 or 80 characters per line for all the above reasons, but also because they have a significant number of readers using text-based email clients such as Mutt. Some Microsoftemail 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.
Servers and client applications
Messages are exchanged between hosts using the Simple Mail Transfer Protocol with software programs called mail transfer agents (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 or IMAP, or, as is more likely in a large corporate environment, with a proprietary protocol specific to Novell Groupwise, Lotus Notes or Microsoft Exchange Servers. Programs used by users for retrieving, reading, and managing email are called mail user agents (MUAs).
Mail can be stored on the client, on the server side, or in both places. Standard formats for mailboxes include Maildir and mbox. 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 IMAP, moving email from one server to another can be done with any MUA supporting the protocol.
Many current email users do not run MTA, MDA or MUA programs themselves, but use a web-based email platform, such as Gmail, Hotmail, or Yahoo! Mail, that performs the same tasks. Such webmail interfaces allow users to access their mail with any standard web browser, from any computer, rather than relying on an email client.
Upon reception of email messages, email client 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 mbox format. The specific format used is often indicated by special filename extensions:
- Used by many email clients including Novell GroupWise, Microsoft Outlook Express, Lotus notes, Windows Mail, Mozilla Thunderbird, and Postbox. The files contain the email contents as plain text in MIME format, containing the email header and body, including attachments in one or more of several formats.
- Used by Apple Mail.
- Used by Microsoft Office Outlook and OfficeLogic Groupware.
- Used by Opera Mail, KMail, and Apple Mail based on the mbox format.
Some applications (like Apple Mail) 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.
URI scheme mailto
Main article: mailto
The URI scheme, as registered with the IANA, defines the 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.
Main article: Webmail
Many email providers have a web-based email client (e.g. AOL Mail, Gmail, Outlook.com, Hotmail and Yahoo! Mail). This allows users to log into the email account by using any compatible web browser 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 Post Office Protocol 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 server. POP supports simple download-and-delete requirements for access to remote mailboxes (termed maildrop in the POP RFC's).
IMAP email servers
The Internet Message Access Protocol (IMAP) provides features to manage a mailbox from multiple devices. Small portable devices like smartphones 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
Messaging Application Programming Interface (MAPI) is used by Microsoft Outlook to communicate to Microsoft Exchange Server - and to a range of other email server products such as Axigen Mail Server, Kerio Connect, Scalix, Zimbra, HP OpenMail, IBM Lotus Notes, Zarafa, and Bynari where vendors have added MAPI support to allow their products to be accessed directly via Outlook.
Business and organizational use
Email has been widely accepted by business, governments and non-governmental organizations in the developed world, and it is one of the key parts of an 'e-revolution' in workplace communication (with the other key plank being widespread adoption of highspeed Internet). A sponsored 2010 study on workplace communication found 83% of U.S. knowledge workers felt email was critical to their success and productivity at work.
It has some key benefits to business and other organizations, including:
- Facilitating 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, telephone call, or conference call 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.
- Helping with synchronisation
- With real time 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 asynchrony: each participant may control their schedule independently.
- Reducing cost
- Sending an email is much less expensive than sending postal mail, or long distance telephone calls, telex or telegrams.
- Increasing speed
- Much faster than most of the alternatives.
- Creating a "written" record
- Unlike a telephone or in-person conversation, email by its nature creates a detailed written record of the communication, the identity of the sender(s) and recipient(s) and the date and time the message was sent. In the event of a contract or legal dispute, saved emails can be used to prove that an individual was advised of certain issues, as each email has the date and time recorded on it.
Email marketing via "opt-in" is often successfully used to send special sales offerings and new product information. Depending on the recipient's culture, email sent without permission—such as an "opt-in"—is likely to be viewed as unwelcome "email spam".
Many users access their personal email from friends and family members using a personal computer in their house or apartment.
Email has become used on smartphones and on all types of computers. Mobile "apps" for email increase accessibility to the medium for users who are out of their home. While in the earliest years of email, users could only access email on desktop computers, in the 2010s, it is possible for users to check their email when they are away from home, whether they are across town or across the world. Alerts can also be sent to the smartphone or other device 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. As of 2011[update], there were approximately 1.4 billion email users worldwide and 50 billion non-spam emails that were sent daily.
Individuals often check email on smartphones for both personal and work-related messages. It was found that US adults check their email 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 the respondents in the study revealed that they check their email on their phone. 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.
Attachment size limitation
Main article: Email attachment
Email messages may have one or more attachments, which are additional files that are appended to the email. Typical attachments include Microsoft Word documents, pdf documents and scanned images of paper documents. In principle there is no technical restriction on the size or number of attachments, but in practice email clients, servers and Internet service providers implement various limitations on the size of files, or complete email - typically to 25MB or less. Furthermore, due to technical reasons, attachment sizes as seen by these transport systems can differ to what the user sees, which can be confusing to senders when trying to assess whether they can safely send a file by email. Where larger files need to be shared, file hosting services of various sorts are available; and generally suggested. Some large files, such as digital photos, color presentations and video or music files are too large for some email systems.
The ubiquity of email for knowledge workers and "white collar" employees has led to concerns that recipients face an "information overload" in dealing with increasing volumes of email. With the growth in mobile devices, by default employees may also receive work-related emails outside of their working day. This can lead to increased stress, decreased satisfaction with work, and some observers even argue it could have a significant negative economic effect, as efforts to read the many emails could reduce productivity.
Main article: Email spam
Email "spam" is the term used to describe unsolicited bulk email. The low cost of sending such email meant that by 2003 up to 30% of total email traffic was already spam. and was threatening the usefulness of email as a practical tool. The US CAN-SPAM Act of 2003 and similar laws elsewhere had some impact, and a number of effective anti-spam techniques now largely mitigate the impact of spam by filtering or rejecting it for most users, but the volume sent is still very high—and increasingly consists not of advertisements for products, but malicious content or links.
A range of malicious email types exist. These range from various types of email scams, including "social engineering" scams such as advance-fee scam "Nigerian letters", to phishing, email bombardment and email worms.
Main article: Email spoofing
Email spoofing occurs when the email message header is designed to make the message appear to come from a known or trusted source. Email spam and phishing methods typically use spoofing to mislead the recipient about the true message origin. Email spoofing may be done as a prank, or as part of a criminal effort to defraud an individual or organization. An example of a potentially fraudulent email spoofing is if an individual creates an email which appears to be an invoice from a major company, and then sends it to one or more recipients. In some cases, these fraudulent emails incorporate the logo of the purported organization and even the email address may appear legitimate.
Main article: Email bomb
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.
Main article: Email privacy
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 information technology 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.
- web bugs invisibly embedded in email content can alert the sender of any email whenever an email is read, or re-read, and from which IP address. It can also reveal whether an email was read on a smartphone or a PC, or Apple Mac device via the user agent string.
There are cryptography applications that can serve as a remedy to one or more of the above. For example, Virtual Private Networks or the Tor anonymity network can be used to encrypt traffic from the user machine to a safer network while GPG, PGP, SMEmail, or S/MIME can be used for end-to-end message encryption, and SMTP STARTTLS or SMTP over Transport Layer Security/Secure Sockets Layer can be used to encrypt communications for a single mail hop between the SMTP client and the SMTP server.
Additionally, many mail user agents do not protect logins and passwords, making them easy to intercept by an attacker. Encrypted authentication schemes such as SASL prevent this. Finally, attached files share many of the same hazards as those found in peer-to-peer filesharing. Attached files may contain trojans or viruses.
Flaming occurs when a person sends a message (or many messages) with angry or antagonistic content. The term is derived from the use of the word "incendiary" to describe particularly heated email discussions. The ease and impersonality of email communications mean that the social norms that encourage civility in person or via telephone do not exist and civility may be forgotten.
Main article: 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 their email inbox is full, and that they are in the process of clearing out all the messages. Harvard University law professor Lawrence Lessig is credited with coining this term, but he may only have popularized it.
Originally Internet email was completely ASCII text-based. MIME now allows body content text and some header content text in international character sets, but other headers and email addresses using UTF-8, while standardized have yet to be widely adopted.
Further information: International email and Email address § Internationalization
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 IETF introduced Delivery Status Notifications (delivery receipts) and Message Disposition Notifications (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 3885 through 3888.)
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 if so, this indicates to a spammer that it is available to be spammed.
- If the spammer uses a forged sender email address (email spoofing), 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 web bugs have been developed. However, these are often seen as underhand or raising privacy concerns, and only work with email clients that support rendering of HTML. Many mail clients now default to not showing "web content".Webmail providers can also disrupt web bugs by pre-caching images.
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