E-mail (Electronic Mail)

Content of the lesson:

E-mail (Electronic Mail)

This is a basic network service used for mutual communication between users of a network (home, company or inside Internet). The owner of a mailbox (and e-mail address) is allowed to create, send and receive messages including attached files, use his directory or participate at electronic conferences etc.

History

Electronic mail was founded intentionally as a very simple service designed for transferring small and exclusively text messages. Of course programmers expected usage of ASCII code (suitable for English but not for Czech which uses diacritical marks).

As the time passed and electronic mail became more popular it was improved in many ways. Support for more languages (character sets) was introduced, the way of adding attachments was unified and also the repertoire of formats which could be used for the content of a message was extended. Thanks to these changes the electronic mail became much more universal service which was used as a platform for offering additional services.

Description

The principle of electronic mail is that a user has dedicated memory space (mailbox) for incoming and outgoing mail at a mail server of his provider (ISP – Internet Service Provider). To be able to read his messages he has to connect to this server and save messages to his computer. The size of mailbox is limited and differs according to the price.

The exact place where a message should be send is recognized from the electronic address in the heading of a message. The heading contains information about the identification of computer where an email should be delivered and also the name of the recipient.

Recipient finds new messages usually after launching a special program (e-mail client). The process of receiving e-mails is done also without the presence of user - the server runs a program which saves all incoming messages and allows all users to read them later.

The recipient has several possibilities how to handle with his message. He can simply read it on screen, print it or save it to file, he can forward it to another user, use the sender address to write a response, etc. He also can delete messages which are not interesting for him or which bother him.

E-mail Address

Each user of this service has his address of electronic mail. The address consists of two parts - username which is unique within the server, then the @ sign and the name of server which is followed by an extension (.cz for Czech servers). The address cannot contain spaces or characters with diacritical marks. A dot is allowed inside the username. For example:

svetlik@gjszlin.cz

this means that a mailbox for user svetlik was created at the server gjszlin.cz. One user can have many addresses and mailboxes at different servers.

Electronic addresses allow you to add additional comments as their content - this is usually used to add a real name. Practically it is done by adding a text in rounded brackets after the text of address or this text is inserted before and the e-mail address is inserted into angle brackets <...>. An alternative form of email address which was mentioned before could be one of the following ones:

To: svetlik@gjszlin.cz (Jaromír Světlík)

To: Jaromír Světlík

Structure of Message

E-mail messages usually consist of these parts:

• header – subject of message, sender, recipient and other information about about e-mail
• body – the message
• attachment – optional part

Header

The header contains particular number of definitions for message attributes (address, subject, etc.) which are added in the following order: name or attribute, semicolon and the value of attribute.

A typical header of electronic message contains at least 4 arrays:

• From – sets the back address of sender (is added automatically)
• To – the same purpose as full address of recipient which is written at post envelopes. This address contains the name (user identification on his computer) but also the location of computer where should the message be delivered. You can use more addresses at once.
• Subject – contains the text which shortly characterizes the content of electronic mail. Using this item it is much easier to orient yourself in your inbox.
• Date – this field contains the date and time when the message was sent, is usually added automatically. It usually contains information about the time zone.

Example of a header:

From: Jaromír Světlík
To: Michal Miklas
Subject: Pozdrav
Date: Wed, 24 Feb 10 01:24:00 +0100

Additional attributes which can be found in header:

• Cc – carbon copy – addresses where a copy should be sent. The label "carbon copy" is used because typing machines used carbon paper to create copies. The message will be sent to all e-mails written here.
• Bcc – blind carbon copy – this creates a hidden copy - te recipient will see e-mails in field "To" and "Cc" but not in "Bcc"
• Received – analogy of post stamps on an envelope. When delivering a message information about all computers where the message went through is recorded with exact times.
• Reply-To – allows you to specify an address where the response should be sent if this address is not identical with the sender.
• Content-type – information about the way how the message should be displayed (usually MIME type is automatically added)

The header cannot contain any fatal mistakes which could not be repaired for correct delivery. These fields are usually prepared and filled by programs which are used for composing and sending messages.

Body

The introduction of MIME standard (Multipurpose Internet Mail Extensions) brought the possibility to use "richer" formats of text inside the body. In the past only plain text e-mails could be sent without any adjustments, types or sizes of fonts, images etc. but nowadays an email message can contain practically the same as a simple web page - for example wrapping to columns, different fonts, illustrations etc. This possibility is used especially for sending several electronic periodicals using the electronic mail.

Attachment

Thanks to the MIME standard you can add any non-text attachments to the email messages.

It is also possible to attach more files to one message. However, you should pay attention because transferring large files might fill the mailbox of the recipient. To transfer larger files (in MB) you should use other services of the Internet like FTP.

Communication Protocols

They are used for communication between computer and mail server and between mail servers. POP3 or IMAP protocols are used for incoming mails and SMTP protocol is used for outgoing mails.

POP3 (Post Office Protocol 3)

This protocol allows downloading electronic mail from the mailbox at mail server to end users. It is suitable for users who work with their mail on one computer. All mail is downloaded to the local drive and after disconnecting from the Internet all emails are available.

There is a large disadvantage because this protocol downloads mails without knowing the recipient and sender. This can be a problem in case that a mailbox is shared by more users and they get messages with universal "To" header (for example from conferences). In this case the IMAP protocol is better.

IMAP (Internet Message Access Protocol)

The protocol IMAP is suitable for users who have to access their email on more computers. E-mails are saved at server and they can access them and manipulate with the electronic mail on that server, archive it to a local computer because the IMAP protocol only downloads headers compared to POP3 which downloads the whole messages. IMAP allows connection of many users to one mailbox (unlike the POP3). The last version is IMAP4.

After disconnecting from a computer network the emails are not available in case that the offline mode is not activated inside your mail client.

SMTP (Simple Mail Transfer Protocol)

SMTP protocol is designed for transferring messages from client to mail server and between mail servers.

It is an Internet protcool designed for transferring electronic mails between stations. This protocol delivers mail using a direct connection between the sender and the recipient. The message is delivered to your mailbox and you can access it later (read mails) using POP3 or IMAP protocols.

Graphical diagram of e-mail communication:

• How e-mail works? - czech version (www.urazydeti.cz)

Programs for Working with E-mails

A client program is used to work with electronic mail. It is used for creating, editing, reading and sending emails. You have to set all parameters of connection with a server which provides the incoming and outgoing of your mail. Mail clients provide a particular comfort because you can set to automatically sort emails according to the sender or create a sending groups to send emails to more users at once.

There are many programs to work with e-mails which are based on the principle client – server.

• MS Outlook Express (integrated in OS Windows)
• MS Outlook (part of the office package MS Office)
• MS Exchange
• Thunderbird
• Pegasus Mail
• Netscape Messenger
• Lotus Mail

When the WWW service was spread several freemail services were founded. These services offer using free electronic mail in a web browser.

• Hotmail.com
• GMail.com
• Email.seznam.cz
• User.centrum.cz

Each post client has to be able to:

• Reply(RE)
• Forward (FW)
• Add attachment (Attachment)
• Automatic response
• Confirm delivery
• Add signatures

Spam

Spam is unwanted advertising mail. Low costs for sending emails allow spammers to send hundreds of millions mails daily using a cheap internet connection. Hundreds of active spammers cause overloading computers in the Internet which usually get tens or hundreds of unwanted emails each day. Spammers get addresses using different ways, for example from internet pages, forms on www or using the try-fault method, ...

Mass distribution of unwanted mails using the electronic mail is in professional terminology called as spamming.

The reasons are clear - money. Spammer who sends spams hopes that several people will response and buy the advertised product or service.

Most of nowadays e-mail servers have their antispam filter which helps you to be protected from unwanted mails. However, the success is not 100%.

Spam is harmful especially because

• it takes place in mailbox and extends the time for downloading mail (= raises the price you pay for your Internet connection)
• you have to spend time to separate spam and common mail and to delete spam
• you can delete a common mail between spam
• SMS message sent to cell phone that you have a new email has no sense anymore
• overloads computer links and mail servers, the costs of spam protection are higher as well as costs for running an e-mail server
• automatic detection of spam might accidentally delete a common email - the reliability of e-mail is lower
• antispam filters can cause the mail to be delivered later (in hours)

Hoax

Another type of e-mail messages is co called hoax. This is name for false string messages which are send around the Internet - they contain false, distorting information, adjusted semi-truths or mix of lies.

A classical text of hoax usually contains these points:

• Description of danger – false danger is shortly described, in case of virus also the way of distribution is described
• Destructive effects – this point depends on the fantasy of the author. Destructive effects can be common as formatting disk or less believable - HDD will start spinning in the other direction, explosion of computer...
• Reliable sources warn you – in most cases the writer tries to convince the others that this warning came from reliable sources ("IBM and FBI warn you" or "Microsoft warns" etc...)
• Call for further distribution – this point is always a part of hoax! Many inexperienced users think that the message is true and send the message to others. This is the reason why these messages spread so fast.

Hoax usually uses people who are not informed or naive and it tries to manipulate with them. There are several typical types of hoax:

• False alarm – the message manipulates with information (Pay attention, ICQ virus, sent to everyone.) or even encourages you for a destructive task (Delete jbdmgr.exe from Windows, it is a virus.).
• Entertaining – using users who want to be funny or who are superstitious - these messages threaten (If you do not send, you will be unlucky.). An obedient user will get everything he wants.
• Requests – hoax usually tries to act on feelings and asks you to give blood, search for a lost person or asks directly for money.

Sample of HOAX message (taken from www.hoax.cz)

Charging or ICQ

From 1. July the ICQ will cost 50 Kč per month. Fight against it and send this text to at least 15 people from your contact list. In case you do it, press F1 and your flower will be blue which means you will not have to pay anything.

Phishing

Phishing is a fraudulent technique used in the Internet to get sensitive details (passwords, numbers of credit cards, pin codes etc.) from victims of this attack. Its principle is to send e-mail messages which look like official requests of banks or other similar institutions and it asks the recipient to enter his details to a website. This website can look like a correct login page to internet banking and the user enters his username and password into it. These details allow attackers to use his bank account to get rich.

Worms

E-mail worms are used to spread electronic mails. After a computer is infected it starts sending e-mails to various addresses which are taken from the e-mail contact list from the infected computer or by searching through saved files and extracting those strings which look like an e-mail address. The advantage of this procedure is to use the e-mail account of the victim so the mail looks like a reliable correspondence.

A special case are networks Botnet which consist of computers which are infected by a special worm. These computers send SPAM in bulk or make DoS attacks when a command is received. DoS are network attacks which deny access to several services - these attacks block services of networks by overloading their connection which can result in server collapse or terminating running programs on servers.

The content of infected message usually contains the infected program as an attachment or it contains links to web pages which are able to infect the computer of a visitor.

Environmentální okénko

Questions

1. What is the purpose of electronic mail and how can you work with it?
2. What is the structure of an e-mail message?
3. Name and describe common communication protocols?
4. What is SPAM?
5. What is HOAX?