email-not-secret-therefore-4

E-mail privacy, without some security precautions, can be compromised because:

• e-mail messages are generally not encrypted;
• e-mail 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 your e-mail
  messages on their mail servers before they are delivered. The backups
  of these can remain up to several months on their server, even if you
  delete them in your mailbox;
• the Received: headers and other information in the e-mail can often identify the sender, preventing anonymous communication.

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, 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.
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email-how-it-works-2

When Anita composes a message, HAPPY NEW YEAR,

using her mail user agent (MUA), she types in, or selects from an address book, the e-mail address of her correspondent. She hits the "send" button.

1. Her MUA formats the message in Internet e-mail format and uses the Simple Mail Transfer Protocol (SMTP) to send the message to the local mail transfer agent (MTA), in this case smtp.a.org, run by Anita's Internet Service Provider (ISP).
2. The MTA looks at the destination address provided in the SMTP protocol (not from the message header), in this case adheesh@a.org. An Internet e-mail address is a string of the form localpart@exampledomain.com, which is known as a Fully Qualified Domain Address (FQDA). The part before the @ sign is the local part of the address, often the username of the recipient, and the part after the @ sign is a domain name. The MTA looks up this domain name in the Domain Name System to find the mail exchange servers accepting messages for that domain.
3. The DNS server for the b.org domain, ns.b.org, responds with an MX record listing the mail exchange servers for that domain, in this case mx.b.org, a server run by Adheesh's ISP.
4. smtp.a.org sends the message to mx.b.org using SMTP, which delivers it to the mailbox of the user Adheesh.
5. Adheesh presses the "get mail" button in his MUA, which picks up the message using the Post Office Protocol (POP3).

This sequence of events applies to the majority of e-mail users.
However, there are many alternative possibilities and complications to
the e-mail system:

• Anita or Adheesh may use a client connected to a corporate e-mail system, such as IBM Lotus Notes or Microsoft Exchange.
  These systems often have their own internal e-mail format and their
  clients typically communicate with the e-mail server using a
  vendor-specific, proprietary protocol. The server sends or receives
  e-mail via the Internet through the product's Internet mail gateway
  which also does any necessary reformatting. If Anita and Adheesh work for
  the same company, the entire transaction may happen completely within a
  single corporate e-mail system.
• Anita may not have a MUA on her computer but instead may connect to a webmail service.
• Anita's computer may run its own MTA, so avoiding the transfer at step 1.
• Adheesh may pick up his e-mail in many ways, for example using the Internet Message Access Protocol, by 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 when the main mail exchange server is not
  available.
• E-mail messages are not secure if e-mail encryption is not used correctly.

It used to be the case that many MTAs would accept messages for any
recipient on the Internet and do their best to deliver them. Such MTAs
are called open mail relays.
This was important in the early days of the Internet when network
connections were unreliable. If an MTA couldn't reach the destination,
it could at least deliver it to a relay that was closer to the
destination. The relay would have a better chance of delivering the
message at a later time. However, this mechanism proved to be
exploitable by people sending unsolicited bulk e-mail
and as a consequence very few modern MTAs are open mail relays, and
many MTAs will not accept messages from open mail relays because such
messages are very likely to be spam.

Note that the people, e-mail addresses and domain names in this explanation are fictional: see Anita and Adheesh.
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email-origin-1

Electronic mail, often abbreviated to e-mail, email, or originally eMail, is a store-and-forward method of writing, sending, receiving and saving messages over electronic communication systems.

My way of saying "WISH YOU ALL HAPPY 2009!"
What is email?

The term
"e-mail" (as a noun or verb) applies to the Internet e-mail system based on the Simple Mail Transfer Protocol, to network systems based on other protocols and to various mainframe, minicomputer, or internet by a particular systems vendor, or on the same protocols used on public networks. E-mail is often used to deliver bulk unsolicited messages, or "spam", but filter programs exist which can automatically block, quarantine or delete some or most of these, depending on the situation.

E-mail predates the inception of the Internet, and was in fact a crucial tool in creating the Internet. MIT first demonstrated the Compatible Time-Sharing System (CTSS) in 1961. It allowed multiple users to log into the IBM 7094^[16]
from remote dial-up terminals, and to store files online on disk. This
new ability encouraged users to share information in new ways. E-mail
started in 1965 as a way for multiple users of a time-sharing mainframe computer to communicate. Although the exact history is murky, among the first systems to have such a facility were SDC's Q32 and MIT's CTSS.

E-mail was quickly extended to become network e-mail, allowing users to pass messages between different computers by at least 1966 (it is possible the SAGE system had something similar some time before).

The ARPANET computer network
made a large contribution to the development of e-mail. There is one
report that indicates experimental inter-system e-mail transfers began
shortly after its creation in 1969. Ray Tomlinson initiated the use of the @ sign to separate the names of the user and their machine in 1971. The ARPANET significantly increased the popularity of e-mail, and it became the killer app of the ARPANET.

         Source

E-mail - Wikipedia, the free encyclopedia

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