| E-mail is an abbreviation of electronic mail, the name of technology and the service rendered for transferring and receiving electronic messages (called “mails") along distributed (including global) computer networks. The basic difference from other message transfer systems (for example, instant messaging services) differs by the possibility of postponed delivery and the developed (and confused due to prolonged development) interaction system between independent mail servers.
History:
The appearance of email can be dated to 1965 when employees of the Massachusetts Institute of Technology (MIT) Noel Morris and Tom Van Vleck have written the program MAIL for the operating system CTSS (Compatible Time-Sharing System), installed on the computer IBM 7090/7094.
After the appearance of the distributed global system by the name DNS, domain names - user@example.com - the user on machine example.com were used for indicating the address. Simultaneously, reviewing the concepts “on machine” occurred: A dedicated server was used for mails and the regular did not have access to the servers (only administrators had access) and users worked on their computer; in this case, mails were received by the server but not the working computers of users and users received their mails through various network protocols from the server (among the widely used at present - POP3, IMAP, RCP, web interfaces). Simultaneously with the advent of DNS, the reservation system for operating the mail servers was invented and the domain name in the mail address has ceased to be the name of a concrete computer and simply became a mail domain, the maintenance of which was looked after by many servers (probably, physically located on different continents and in different organizations).
Also, other e-mail systems existed (some of them exist even now) such as Netmail in network FidoNET, X.400 in networks X.25. Access to them through the Internet and back was accomplished through a mail gateway.
Modern architecture:
If the mail transfer issues through UUCP are not touched upon, then the modern architecture of the mail servers interaction looks like the following: mail systems, independent of each other, are fixed in various domains. Each mail domain can have several users. (However, actually, one organization or an individual can own many domains, which are served (physically) by a single mail system). Mail is transferred between units with the use of Mail Transfer Agent programs (such as, for example, sendmail, exim4, postfix, Microsoft Exchange Server, Lotus Domino etc.). The behavior of systems while communicating with each other is strictly standardized, for this protocol SMTP is used (and observance of this standard, on the level with public support of DNS by all participants is the foundation for the possibility of communication “from all with all” without preliminary arrangements). Communication of the mail system and users, generally, is not regulated in any way and can be arbitrary, even though both have open as well as close (connected with software of concrete manufacturers) protocols for communication between the users and the mail system. The program, working in the mail system and serving the users, is called MDA (Mail Delivery Agent). In some mail systems, the MDA and MTA can be combined into a single program; MDA and MTA can be diversified in the form of different programs in other systems or generally executed on various servers. The program where the user gains access is called the MUA (Mail User Agent).
Several mail servers, executing both the forwarding of mail within the organization as well as other tasks linked with e-mail can be provided within the given mail system (usually present within a single organization). The other tasks are spam filtration, checking the contents with antivirus, auto reply provision, archiving incoming and outgoing mails and providing access to users through various methods (from POP3 to ActiveSync). The communication between servers within the limits of a single mail system can be a slave to general rules (the use of DNS and mail routing rules with the help of SMTP), as well as follow their own rules of the company (using software).
Relays:
DNS allows in specifying any unit of the internet not necessarily the part of the domain zone of the addressee’s domain as the accepting server (MX-entry). It can be used for adjusting the relaying (transfers) of mails through a third server. The foreign server (for example, is more reliable than the user’s server) receives the mails for the user’s domain and delivers them to the mailing servers of the user as soon as the possibility appears. Historically, control over the “send mail to whom” was not available (or due importance was not given to it) and servers transferred mails to any domains without similar monitoring. Such servers are called “Open Relays” (presently, new open relays are appearing mainly due to the mistakes in server configuration).
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Shocking news today - hackers broke into the Yahoo! e-mail account of Sarah Palin and sent screenshots of her email correspondence to several major blog websites and even Associated Press.
Hackers claim that Palin used Yahoo email, instead of her official Alaska governor email, to hide a lot of her correspondence which she never wished to become public, including emails linked to her records, which she refused to make public. The Secret Service approached The Associated Press requesting the copies of Palin's emails which The AP received from hackers. The AP refused to comply. McCain-Palin camp is furious and demand the full investigation and prosecution of hackers calling this a "shocking invasion of the governor's privacy and a violation of law".
