E-mail is probably the service that has contributed most to the increase in popularity of the Internet so great, still one of the main reasons that people connect to this network.
The key to success lies right in its features: it is fast, very cheap and is an excellent way of communicating with others, because a message can contain any text, images, music or videos. In addition, while an ordinary letter needs days or weeks it should be received, a message would be enough usually a few seconds to reach the other side of the planet.
In terms of privacy, however, things are not so good. Although generally the symbol used to represent the service is a sealed envelope, in reality things are not so at all. A more appropriate symbol for e-mail would be the postcards.
Although a card can not be read by anyone, it is enough to know that the postman can consult before delivery to realize that you should not write your PIN credit card site or a declaration of love secret behind thereof. Similarly, email messages are transferred into network using clear text, which, combined with the slight possibility to intercept them, makes them very vulnerable.
The most common method to protect the e-mail is to encrypt. Two technologies are used in general to do this: PGP (Pretty Good Privacy) and PEM (Privacy Enhanced Mail). Both allow both message confidentiality by encrypting content and verification of the origin using digital signatures.
Encrypt messages, although percentage increased in recent years, remains very little used, making the mail to be considered an unreliable communication medium. Despite this, e-mail incidents are quite rare.
To send and receive electronic messages there are used multiple protocols: SMTP (Simple Mail Transfer Protocol) to transfer messages from the sender to the server, and between servers, ie POP3 (Post Office Protocol) for receiving mail. Another protocol is used for email is IMAP (Internet Message Access Protocol), an improved version of POP3.
In general, the network service provider – ISP (Internet Service Provider) is responsible for creating mailboxes. They have associated one or more e-mail. A mailbox is not only a file server, e-mail, where are collected the addresses associated inbox. When the client connects to the server, is transferring messages from these files on your own computer.
The figure below describes the process that takes place to send a message from George Smith of the Ministry of Transport by John Doe, working at the London branch of IBM:
Steps that are performed are:
1. George compose the message in his mail program (client application). Fill in the recipient field (To: ) the e-mail address of John.
In this program is configured the mail server name that contains his post box (corresponding to the address email@example.com).
2. When you press Send button of the program, it establishes a connection between his computer and port 25, the SMTP protocol corresponding of the server, connection used to send to this the message contents.
3. Mail server receives the message and one of its programs (server application) examines information about the recipient. From address firstname.lastname@example.org cut the server name, ie uk.ibm.com. Using DNS service, find its IP address.
4. Mail server of the Ministry of Transport establishes a direct connection with uk.ibm.com server whose IP address determined in previously step, sending through the established channel the message for Joe.
5. UK server gets the message, validates recipient, verifying that john_doe is really a system user, and stores the message in the electronic mailbox of John.
6. When John PC connects to the Internet and John request receiving mail, client program connects to the server using POP3 protocol (port 110) or IMAP (port 143). With the connection established, from the server is transferred all messages from the last request.
7. Client program of John processes received data and displays them on the screen.