Email

Email, i.e. electronic mail, is one of the oldest and most important internet services.

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An email consists of the content and a Header with additional information. This header consists of several lines, each beginning with a special keyword.

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key	meaning
To:	address
From:	sender
Reply-To:	adress to answer to (can be different fronm sender)
Subject:	short line describing the context
Date:	sending time

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Important part of an email is the address. It has the following form:

NAME@DOMAINNAME

NAME refers to the receiver personally, DOMAINNAME to the computer that receives the message.

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peter@peter-junglas.de

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The To: field of a mail can contain several addresses, separated by a comma.

Mailing list: special address that refers to a group of people. Each mail send to a mailing list, is copied to all members. Mailing lists are created by the mail administrator (postmaster) of a site.

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A mailing list is a (private) forum of discussion. There exist may open lists, where everybody can subscribe by simply sending a special message.

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There is no world wide email phone book. At least one can find the addresses of people, who send mail or write news article, in the header. Email addresses of university employees can usually be found via the homepage of the university or institute.

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The content of an email could simply be an ASCII text. Mails containing other formats (e.g. texts with diacritics, HTML texts or images) are tagged with the corresponding MIME type. Furthermore one can append arbitrary files to a mail (attachments).

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Many people append their address (including phone number or URL of their home page) explicitely to each mail (signature).

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One can send a copy of a mail to other people, using the header field CC: (Carbon Copy).

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All receivers of a mail can see the complete To and CC lists.

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The header field BCC: (Blind Carbon Copy) works like CC, with the difference, that the ordinary receivers can't see the BCC list.

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Many domains have a special mail server that is permanently connected to the internet. This guarantees that incoming mails are stored automatically. The receivers fetch their mails from the server.

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Two different methods are in use to transport mails vom the server to the receiver:

POP

Mails are copied to the computer of the receiver and (generally) removed from the server.

IMAP

Mails remain on the server and can be organized there .

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Lots of programs exist which ease the sending, receiving and organizing of mails, supplying lots of extra functions.

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Some important functions of mailing programs:

• storing mails in folders (directories)
• management of addresses
• Reply function: send a mail to the sender of a given mail
• Forward function: send a received mail to someone else

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Generally mails are open to attack: sender, receiver and content of a mail can be read or changed. Special methods have been developed, which guarantee the identity of the sender and the correctness of the content. They are based on cryptophic methods.