Translated by
2013/07/16 16:33:50

E-mail (e-mail)

E-mail — technology and services in transfer and obtaining the electronic messages (called "letters" or "e-mails") provided by it on distributed (including global) a computer network. The main difference from other message transmission systems (for example, instant messaging services) is the possibility of the postponed delivery developed (and confused because of a progressive tense of development) the system of interaction between independent mail servers.

Content

Names

In addition to the name "e-mail" in the Russian written and oral languages also others are used, being in the majority a calque and/or posterization of the English name:

  • email, mail (a transcription from English).[1]
  • e-mail, email, emayl (different alphabetic tracing-papers from English)
  • soap (in a popular speech, from English "mail")

The correct writing yet not zafisirovanno in dictionaries. The information bureau of Грамота.ру specifies that E. Vaulina suggests to write an e-mail and an e-mail in the My Computer dictionary, but notices that such writing does not meet literary standard, at the same time, in other answer advise to write e-mail with Latin. [2]

Use indicators

During 2010 Internet users sent each other 107 trillion e-mails most of which part was spam. It is said in the report with statistics of the Internet for 2010 from Pingdom company.

On average, in a day users sent 294 billion letters through Network. In total worldwide specialists of Pingdom counted 1.88 billion users of e-mail. At the same time, in a year their number grew by 480 million people. The quantity of email accounts was 2.9 billion. From 107 trillion letters sent in a year, 89.1% were spam.

Mail services

Mail services in Russia

Image:Доли почтовых сервисов в России 2013.png

* Data of TNSWebIndex, May, 2013. All Russia, 12-64 years.

Mail services in the world

Основная статья: Webmail services (world market)

History

Emergence of e-mail can be referred to 1965 when the staff of the Massachusetts Institute of Technology (MIT) Noel Morris and Tom Van Vlek wrote the MAIL program for the CTSS operating system (Compatible Time-Sharing System) installed on the IBM 7090/7094 computer.

The general development of e-mail went through development of local interaction of users on the multi-user systems. Users could, using the mail program (or its equivalent), to send each other messages within one mainframe (computer). The next step was in an opportunity to send the message to the user by other machine — the indication of a name of the machine and a user name by the machine was for this purpose used. The address could register in the form of foo! joe (the user of joe on the foo computer). The third step for formation of e-mail occurred at the time of emergence of transfer of letters via the third computer. In case of use the UUCP address of the user included a route to the user via several intermediate machines (for example, gate1! gate2! foo! joe is the letter for joe via the machine gate1, gate2 on the machine foo). A lack of such addressing was the fact that the sender (or to the administrator of the machine on which the sender worked) needed to know an exact way to the addressee's machine.

After emergence of the distributed global system of names DNS, for the indication of the address domain names — user@example.com — the user of user by the machine example.com began to be used. Along with it there was a reconsideration of a concept "by the machine": for mail dedicated servers on which normal users had no access (only administrators) began to be used, and users worked on the machines, at the same time mail came not to working machines of users, and to the mail server from where users took away the mail according to different network protocols (among extended currently — POP3 IMAP MAPI web interfaces). Along with emergence of DNS the restoration system of delivery routes of mail was thought over, and the domain name in the postal address stopped being a name of the specific computer and became just mail domain for which service many servers could be responsible (perhaps, physically placed on different continents and in the different organizations).

Besides, existed (and exist on this moment) and other systems of e-mail (some of them exist and now), somehow Netmail in network FidoNET, X.400 in networks X.25. Access to them from the Internet is also back performed through mail gateway. For routing of mail in networks X.25 in DNS it is provided special resource record with the corresponding name X25 (code 19).

Modern architecture (SMTP)

The commonly accepted exchange protocol in the world e-mail is SMTP Simple Mail Transfer Protocol - the Simple mail transfer protocol (привет, the mail transfer protocol). In the commonly accepted implementation he uses DNS for determination of rules of transfer of mail (though in the private systems, like Microsoft Exchange, SMTP can work proceeding from information from other sources).

In different domains the mail systems are configured, independent from each other. Each mail domain can have several users. (However, actually, can be so that one organization or the person owns many domains which are serviced (physically) by one mail system). Mail is transferred between nodes using programs of transfer of mail (Шаблон:To lang-en) (Such as, for example, sendmail, exim4, postfix, Microsoft Exchange Server, Lotus Domino , etc.). The behavior of systems at communication is with each other strictly standardized, the SMTP protocol is for this purpose used (and observance of this standard, on an equal basis with general support of DNS by all participants, is a basis for a possibility of communication "all with all" without preliminary arrangements). Interaction of a mail system and users, generally, is not regulated in any way and can be any though there are both open, and closed (tied on software of specific producers) protocols of inter-user communication and a mail system. The program working in a mail system and servicing users is called MDA (привет, the agent of mail delivery). In some mail MDA and MTA systems can be united in one program, in other systems can be carried in the form of different programs or in general be executed on different servers. The program using which the user provides access is called MUA though, in case of, for example, web interfesa, can be absent.

In the set mail system (which is usually within one organization) there can be a set of the mail servers executing both transfer of mail in the organization and another, connected with e-mail tasks: spam filtering, check of investments an antivirus, providing an auto answer, archiving of the entering / outgoing mail, providing access to users by different methods (from POP3 to ActiveSync). Interaction between servers within one mail system can be as it is subordinated to the general rules (use of DNS and rules of a marshurtization of mail using the SMTP protocol), and to conform to own rules of the company (the used software).

Rayleighs

DNS allows to specify any node of the Internet which is not necessarily a part of a domain zone of the domain of the receiver as the accepting server (MX record). It can be used for setup of a releing (transfer) of mail via the third servers. The third-party server (for example, more reliable, than the user's servers) accepts mail for the domain of the user and sends it on mail servers of the user as soon as an opportunity appears. Historically, control of that, "to whom to send" mail was not (or did not attach it due significance), and servers without similar control transferred mail to any domains. Such servers are called open rayleighs (now new open rayleighs appear generally from behind errors in configuring of the server).

For the users servers of a mail system are rayleighs (users send mail not to servers of a mail system of the addressee, and to "the" mail server which transfers letters further). In many networks of providers of the Internet an opportunity to send letters under the SMTP protocol out of limits of network is closed (because of use of this opportunity by trojans, viruses). In this case the provider provides the SMTP server via which all mail out of limits of network goes. An open rayleigh at the same time such rayleigh which does not check whether the user is "" is considered (check can be performed both on the basis of the user's address, and on the basis of identification by the password/certificate).

Routing of mail

The mail server, when processing the letter, operates on the following algorithm: for the domain receiver all MX records are looked for. They are sorted in decreasing order of a priority. If the address of the mail server matches one of the nodes specified in MX records, then all records with a priority smaller to a node priority in mx-record (and also MX record of the node) are discarded, and delivery is performed on the first answering node (nodes are tried in decreasing order of a priority).

If the network has different DNS servers (for example, external — on the Internet, and local — in own limits), then the situation when "internal" DNS servers as the most priority receiver indicate the unavailable server on the Internet where mail from the rayleigh specified as a node receiver for the Internet is redirected is possible. Similar separation allows to perform routing of mail by the general rules between the servers which do not have Internet connection.

In case of Microsoft Exchange, for routing of mail between several servers in an organzation information on receivers from the Active Directory is used. Versions of Microsoft Exchange 2000, 2003 use a concept group of routing (and the connectors set manually between groups), since Exchange 2007 routing is performed proceeding from information on Active Directory topology (i.e. routing is performed according to settings of replication between the Active Directory nodes) [3]

The Proofpoint Sendmail mail server supports the file of the mailertable configuration allowing to set rules of transfer of mail passing[4].

Structure of the letter

The e-mail consists of the following parts:

  • The headings of the SMTP protocol received by the server. These headings can join, and can not join in a letter body further so the situation when the server has bigger information on the letter is possible, than contains in the letter (so, for example, the RCPT TO field specifies the receiver of the letter, at the same time in the letter the receiver can be not specified). This information is transferred out of server limits only within the SMTP protocol, and change of the protocol on delivery can lead mails (for example, on a node receiver during internal routing) to loss of this information.
  • The letter (in terminology of the SMTP - 'DATA' protocol) which in turn consists of the following parts separated by blank line:
  • Letter headings. In the letter the service information and marks of mail servers through which there passed the letter, marks about a priority, the instruction to the address and a name of the sender and receiver of the letter, a subject of the letter and other information is specified.
  • Letter bodies. In a body of the letter there is, actually, a text of the letter. According to the standard, in a body of the letter there can be only characters of ASCII. Therefore when using national codings, different data representation forms (HTML, RTF, binary files) the text of the letter is coded according to the MIME standard and cannot be read by the person without use of the decoder or an e-mail client.

Heading SMTP

The heading SMTP comprises the following information:

  • the name of the sending node (not a name of the sender, but server name or the computer of the user who addressed the server) - the parameter of the message HELO/EHLO which is usually complemented with "objective" information the server (HELO may contain any name, and IP of the sender to forge significantly more difficult), to the IP address is performed search of PTR signing up in DNS, all this together allows to identify the sender at the network layer (and in reality it is often used for check of reliability of the sender using black/white lists, including on the Internet - cm of RBL).
  • The MAIL FROM: field containing an email a source address. The address can be any (including from nonexistent domains, however this address can be also checked at primary check for spam).
  • The RCPT TO: field is the most important field for mail delivery, contains the e-mail address of the receiver. The majority of the mail systems in case of an opportunity checks whether there is a user and can refuse to accept mail if the user specified in RCPT TO does not sushchesvut.

Letter heading

The heading of the letter is described by the RFC standards:

The heading separates from a letter body blank line. The heading is used for journalizing of passing of the letter and office marks (sometimes lines of journalizing and a mark are called kladzha). In Microsoft Outlook this heading is called Headings of the Internet (it is meant that each line - separate heading). Are usually specified in heading: mail servers through which there passed the letter (each mail server adds information on that from whom it received this letter), information on whether this letter is similar to spam, information on check by antiviruses, the level of urgency of the letter (can change mail servers). Also the program using which the letter was created is usually written in heading. Most often e-mail clients hide headings from the user at normal use by a mail system, but give an opportunity to see headings if there is a need for more detailed analysis of the letter. If the letter from a SMTP format is converted into other format (for example, into Microsoft Exchange 2007 of the letter are converted from a SMTP format into MAPI), headings remain separately, for a possibility of diagnostics.

Headings are added from below up (i.e. every time when it is necessary to add heading to the message, it is finished in the first line, before all previous).

In addition to the service information, letter headings store also information shown to the user, it is normal the sender of the letter, the receiver, a subject and date of sending.

The most often used headings

  • Return-Path (RFC 821, RFC 1123) is the return address. Can differ from MAIL FROM. (i.e. the return address can be ukazn other than a source address).
  • Received (RFC 822, RFC 1123) is a line of journalizing of passing of the letter. Each mail server (MTA) marks processing with this message. If the message passes through several mail servers (a normal situation), then new messages are finished over previous (and the magazine of movement is read upside-down, from the next node to the most distant).
  • MIME-Version (RFC 1521) is the version of MIME with which this message is created. As the message is created before all other events with the letter, this heading usually very first (i.e. the last in the list).
  • From: (RFC 822, RFC 1123, RFC 1036) is the Name and a source address (in this heading the text box with a name of the sender appears). Can not match return-path and not match even the heading SMTP MAIL FROM:.
  • Sender: (RFC 822, RFC 1123) - the Sender of the letter. It is added for an opportunity to specify that the letter from someone's name (from) is sent by other person (for example, the secretary on behalf of the chief). Some e-mail clients show the message in the presence of sender and from as "the message from 'sender' on behalf 'from'". Sender is information heading (and can also differ from the heading SMTP MAIL FROM).
  • To: (RFC 822, RFC 1123) is the Name and a destination address. Can contain several times (if the letter is directed to several receivers). Can not match the SMTP RCPT TO field.
  • cc: (RFC 822, RFC 1123) — (from привет). Contains names and the addresses of secondary poluchayetel of the letter to which the copy goes.
  • bcc: (RFC 822, RFC 1123) - (from привет). Contains names and the addresses of receivers of the letter whose addresses should not be shown to other receivers. This field is usually processed by the mail server (and leads to emergence of several different messages at which bcc supports only that receiver to whom the letter is actually directed). Each of poluchayetel will not see in this field of other receivers from the bcc field.
  • Reply-To: (RFC 822, RFC 1036) is a name and the address where it is necessary to address answers to this letter. If, for example, the letter is sent by a bot, then as Replay-To the address of the person ready to accept the answer to the letter will be specified.
  • Message-ID: (RFC 822, RFC 1036) is a unique identifier of the message. Consists of the address of a node sender and number (unique within a node). The algorithm of generation of unique number depends on the server/client. Looks approximately so: AAB77AA2175ADD4BACECE2A49988705C0C93BB7B4A@exapmle.com. Together with other identifiers it is used for search of passing of the specific message in magazines of a mail system (the mail systems fix passing of the letter on its Message-ID) and for the instruction on the letter from drukhy letters (it is used for grouping and creation of chains of letters). It is usually created by the first mail server (MTA) at the time of acceptance of mail from the user.
  • In-Reply-To: (RFC 822) - indicates Message-ID for which this letter is the answer (using it e-mail clients can easily build a correspondence chain - each new answer supports Message-ID for the previous message).
  • Subject: (RFC 822, RFC 1036) is a letter subject.
  • Date: (RFC 822, RFC 1123, RFC 1036) is date of writing of the letter.
  • Content-Type: (RFC 1049, RFC 1123, RFC 1521, RFC 1766) is letter contents type. Using this field the type (HTML, RTF, Plain text) contents of the letter and coding in which the letter is created (cm lower about codings) is specified.

In addition to standard, mail servers (and robots on processings of mail) can add the own headings beginning with X-(for example, "X-MyServer-Note-OK" or "X-Spamassasin-Level").

Letter body

The body of the letter separates from heading blank line, and comes to an end (according to the SMTP Simple Mail Transfer Protocol standards - the Simple mail transfer protocol) with the line consisting of the only point (and a newline character). A part of e-mail clients (for example, Thunderbird) show this point, a part does not. In a не-smtp standards the format of the letter depends on the standard of a system (for example, MAPI), but before "release" of the letter out of limits of a MAPI compatible system (for example, before transfer via the Internet) is usually given to a SMTP compatible type (otherwise routing of the letter would be impossible as the standard of mail transfer on the Internet is SMTP).

One of significant restrictions of standards for mail transfer is use of 7-bit coding (ASCII). For the English text it does not represent a major issue, however, the majority of not English-speaking languages use 8 (and more) bit codings which transfer without distortions is not guaranteed. For the purposes of compatibility, all not 7-bit codings are given to a 7-bit type (using different encoding techniques of the text).

Chains of letters

Thanks to existence in the letter of a unique identifier, and also to the fact that the vast majority of e-mail clients at the answer to the letter copy its identifier in the field of "In-Reply-To" ("in response to") there is a possibility of reliable grouping of letters on a chain (привет). In different e-mail clients it is implemented on a miscellaneous, for example, Microsoft Outlook allows to find all connected with set letters; the Gmail web interface groups messages on the basis of data on a chain in a uniform object. Some e-mail clients (for example, mutt) allow to structure the chains (which are formed usually in mailings when many subscribers) in the form of a tree participate in a conversation (the question generated several answers, on each of which gave the comment - it created several branching lines). Also such clients usually are able to cut compulsorily chains when changing a subject of the message (including that change of a subject of the message means new discussion though, perhaps, and caused by the previous conversation).

Mailings

A mail system allows to organize the complex systems based on transfer of mail from one-to-many to subscribers, it:

  • Mailings — the letter from one address with identical (or changing on a template) contents, sent to subscribers of mailing. It can be technically organized as sending a set of letters (it is used by sample letters) or as sending the letter with a great number of poluchayetel (in the TO, CC, BCC fields). For management of large mailings (more than 10-50 subscribers) specialized programs are used (for example, mailman). Correctly organized mailing should control return of letters (messages about impossibility to deliver the letter) with an exception of unavailable addressees of the mailing list, to allow subscribers to unsubscribe. Undesirable mailings are called spam and significantly complicate functioning of the mail systems.
  • Groups of correspondence — specialized type of mailing in which the letter to the group address (the normal postal address in which processing of mail the specialized program is engaged) is sent to all participants of group. Is an analog of news conferences, echo conferences. Correctly configured mailing should control cycles (two robots of mailings signed at each other are capable to create an infinite loop of transfer of letters), to limit the participant list of mailing, having the right to the premises of the message, to fulfill the other requirements to mailing.

For management of mailings managers of mailings are used. In addition to maintaining the address list and accomplishment of sending of the set message they provide filtering of letters, possibilities of pre-moderation of letters before the premises in mailing, maintaining archives, management of the subscription/formal reply, mailing of digests (short contents) instead of all amount of mailing.

Examples of management programs for mailings:

Spam

E-mail (on an equal basis with the news usenet groups), in process of growth of popularity, began to be used for mailing of not requested advertizing messages, how advertizing brochures by mail are scattered. However, unlike the essential cost of paper mailing, sending a significant amount (up to millions) messages is practically possible to the sender. It led to the disproportionate growth of quantity and the amount of advertizing mailings. In process of toughening of prohibition on advertizing, messages were separated into legitimate newsletters (to which the user and which he can refuse at any time) and illegitimate (actually, and called by spam) usually subscribes. For spam sending all possible technical tricks (open rayleighs, botnets, counterfeit messages about impossibility of delivery, the proxy servers, servers of free mail allowing automation of sending mail) at the moment are actively used.

According to Pingdom company, from 107 trillion letters sent for 2010, 89.1% were spam. Different mechanisms were developed for fight against spam (the black lists of senders, gray lists (requiring the repeated address of the mail server for sending), contextual filters). Probability "wrong positive" solutions concerning spam became one of effects of implementation of means of fight against spam (a part of the letters which are not spam began to be marked as spam). In case of aggressive it leads an antispam policy (destruction of the letters seeming spam in the automatic mode without notice of the sender/receiver) to hardly detectable problems with passing of mail (since messages are removed or pass depending on heuristic algorithms).

E-mail according to the SaaS model

SaaS- solutions in the field of e-mail is that basic service which works in the companies of any scale. One of interesting offers is a set from Microsoft Hosted Exchange and Symantec Hosted Email Security.

Advantages to the client who will work according to the SaaS model are quite noticeable - it is rapid implementation, low cost of the solution due to lack of purchase costs of the server hardware and the software and also lack of need to expand own IT infrastructure for service of solutions. The basic cost of "the entrance ticket" for the companies with number of users to 24 will be 300 rub a month, further – the more, the cheaper (if it is more than hundred accounts – already of 245 rub). The company will receive 3 GB of the place on each mailbox, setup of service, integration for it as with AS&AV-сервисами, and other software of Microsoft company, user training and access to call center for the solution of all technical issues. The similar situation and with Symantec Hosted Email Security which will spam-protect corporate e-mail of viruses and other undesirable contents – its cost will make 80 rub for each user in a month.

The era e-mail comes to an end?

For the time being Facebook in your workplace can be prohibited, but more and more companies provide to the employees of function of chats, posts and comments on corporate social networks (Enterprise Social Software, ESS). Such platforms of joint work as Cisco Quad, Yammer, Jive, Traction Software, Socialtext, SocialCast, Salesforce.com Chatter, WizeHive (and dozens of others) give to employees the chance to discuss the ideas, to work together on documents, to send news and to ask questions using posts, chats, microblogs and forums. Some of the listed applications – for example, Cisco Quad – include the "voice over IP" functions (VoIP) for support of voice and video conferences in real time and also the mobile applications supporting joint work in the mobile and remote modes.


However, let's ask ourselves a question: whether really corporate social networks help the companies to increase labor productivity and to improve financial performance? According to Gartner analytical company, in 2011 costs for corporate social applications on a global scale can make 770 million US dollars that is 16 percent more, than a year before (this indicator does not include the means of ESS used for customer interaction and external partners). It is a drop in the ocean in comparison with costs for traditional software tools for joint work, such as e-mail (e-mail), systems of exchange of documents, means of calendar work and web conferences. This market is a little amorphous, but, according to some industry reports, only in the USA its volume is about 5 billion dollars a year.

If, as expected, the enterprises take of more flexible style of communications (individual subscribers already use it) advantage and will refuse e-mail for benefit of the posts extended in real time, long-term perspectives of ESS will become very tempting. According to forecasts of Gartner company, in the next three years corporate social applications will become the main instrument of communications and will replace e-mail in 20 percent of the companies. Many organizations already realized advantages of ESS.

Students and teachers of faculty MBA of Duke University (Duke University, the USA) use the solution of Cisco Quad for joint work over projects in different time zones. Students from the USA, Great Britain, Dubai, India, China, Russia use Cisco Quad for formation of the virtual working groups, search of people with common interests, file sharing and video records with the students working on similar projects and instant video conferencing and chats. Teachers use this platform for transfer of lectures in real time through web castes and for providing training materials to students in video clips and interactive formats with broad functionality.

Though it is difficult to formalize many advantages of ESS (employees feel more comfortably? labor relations became stronger? joint work gained bigger distribution?), these technologies have the mass of notable advantages. In one of development teams after implementation of corporate social networks the number of e-mail messages was reduced by 38 percent, and the average size of such messages decreased by 43 percent. Moreover, using ESS product managers began to save weekly 7.8 hours, and engineers - 5.4 hours. The released time gave them the chance to solve more important problems.

Nevertheless on a propagation path of ESS there are a lot of obstacles. One of problems – resistance of employees. Already today each employee should use on average at least six "productivity applications". One more such application in the form of ESS is too.

Before IT departments there is other problem – need of integration of corporate social networks into the existing infrastructure. By the end of 2011 more than a half of the enterprises in the USA and Europe will implement corporate social technologies, but only units of such technologies "at least will be far off connected to business systems, applications and procedures", the author of the independent report of Forrester Research research firm published in April, 2011 "Integration claims: new problem of corporate social products" (Integration: The Next Frontier For Enterprise Social). "Except for several companies pioneers, said in the report, – the isolated, autonomous social technologies remain regulation".

Commercial use

Step-by-step passing of e-mail from the sender to the receiver (without use of proxy of the server):

  1. Creation of the letter;
  2. Connection of an e-mail client with SMTP Simple Mail Transfer Protocol - Simple transfer protocol of mail server of the sender;
  3. Transfer to the SMTP server of information on the one to whom mail intends and who is a sender;
  4. Check by the SMTP server of correctness of data on the addressee and the sender and adoption of the letter (with headings and a body of the letter);
  5. Setting of the letter in delivery queue;
  6. the DNS query about mail servers (MX record) for the domain of the addressee;
  7. Attempt of connection of the SMTP server of the sender with the mail servers of the addressee having the greatest priority. If the attempt is unsuccessful, still attempts of connection with standby mail servers of the domain of the addressee become;
  8. Transfer of the letter in case of successful connection with the mail server of the domain of the addressee, or setting in queue for attempt to send the letter later, in case of failure;
  9. Acceptance by the SMTP server of the domain of the addressee of the letter
  10. Verification of the letter regarding its similarity to spam
  11. Transfer to its module which is engaged in storage of letters and issue to their addressees under the protocol POP3, IMAP or another;
  12. Connection of the addressee with POP3 or IMAP the server, authentication and a receipt of the letter by the addressee.

E-mail servers with number of accounts it is more than 10 million

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Transfer protocols of e-mail

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Popular programs for work with E-mail

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See Also

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Links

  • RFC 822 — Standard for ARPA Internet Text Messages
  • RFC 2142 — Mailbox Names for Common Services, Roles and Functions
  • RFC 2368 — The mailto URL scheme
  • RFC 2822 — Internet Message Format

Notes

  1. Грамота.ру
  2. Questions No. 195511 and 220471 in information bureau of gramota.ru [1]
  3. Rand Morimoto, Michael Noel, Andrew Abbeyt, Chris Amaris, Mark Vaynayrdt, Microsoft Exchange 2007 the complete management, the lane with engl. Ya.P. Volkovsky, N.A. Mukhina, S.A. Shestakova, Williams, 2008 ISBN 978-5-8459-1343-2 (ISBN 0-672-32920-4 English).
  4. DNS Using 'mailertable' in Sendmail