E-mail is the oldest and most widely used Internet service. E-mail stands for "electronic mail" and is used to exchange digital messages. It consists of an e-mail header and an e-mail body - the actual content.

Today, e-mails are mainly transmitted via SMTP and IMAP 4 or POP 3. The sender or recipient addresses associated with the e-mail look like this: info@mail.co.uk. In this example, "info" is the so-called local part and "mail.co.uk" is the so-called domain part.

Communication via e-mail consists of several components: Mail User Agents, Mail Transfer Agents and Mail Delivery Agents. The mail user agents are the familiar e-mail clients and are used to read, compose, send and receive e-mails. Mail User Agents cannot communicate with each other. If an e-mail is sent via a mail user agent, it first reaches a mail transfer agent (MTA for short). This is typically an SMTP server that receives and forwards e-mails. If the recipient address does not belong to the same domain part of the own e-mail address, the e-mail is forwarded to the MTA that is responsible for the corresponding domain part and then forwarded to the Mail Delivery Agent (MDA for short). This is typically an IMAP or POP 3 server that can be accessed via the recipient's mail user agent.

E-mail attachment

An e-mail attachment can be thought of as an enclosure in a letter. However, an e-mail is a file that is sent from the sender to the recipient. This is made possible by the MIME protocol (Multipurpose Internet Mail Extension), which is designed to allow audio, video and binary files to be transmitted via e-mail without having to convert the files into the 7-bit ASCII format in which e-mails were originally transmitted.

It is important to note whether the recipient has the appropriate programme to open the file and the maximum attachment size allowed by the e-mail service. This applies to both the sender and the recipient. If e-mails including attachments are too large and cannot be delivered, you will receive a bounce message. A bounce message is an error message that is automatically generated by a mail server in the case of undeliverable e-mails.

E-mail filters

The configuration of e-mail filters is intended to facilitate the handling of incoming e-mails. These can be filtered according to sender, recipient, subject, CC, BCC and components of the content and moved to separate folders. Furthermore, e-mails from individual senders can be marked as spam or unwanted advertising, so that future e-mails from the sender can be filtered, moved to appropriate folders or deleted altogether. E-mail filters can be used not only for automatic moving or deleting of e-mails, but also for direct forwarding or automatic replying to e-mails that meet the corresponding filter conditions.

The procedure for creating e-mail filters differs from e-mail provider to e-mail provider. Typically, the filter function can be found under "Settings".

E-mail header, e-mail address, CC and BCC

An e-mail consists of a header and a body (content of the message). The header contains the sender and the date the e-mail was sent. In addition, the e-mail header can contain information about the recipient and the content of the message. This information is not necessary for the technical delivery, because sender and recipient are also transmitted by the so-called envelope sender and envelope to.

As a rule, e-mail clients display the following information of the e-mail header:

  • Sender
  • Recipient
  • CC: additional recipients
  • Subject
  • Time of creation

The e-mail addresses of sender and recipient look like this: info@mail.co.uk. In this example, "info" is the so-called local part and "mail.co.uk" is the so-called domain part.

CC stands for Carbon Copy. It is a copy that is sent to one or more email addresses besides the recipient. Typically, those who receive an e-mail as a CC are told that the e-mail is not directly addressed to them, but is merely for their attention or information. E-mail addresses in the CC field are visible to all recipients of the e-mail.

E-mail addresses in the BCC field are not visible to any of the recipients. BCC stands for Blind Carbon Copy and is usually used for information purposes and as a control mechanism for superiors, for example.

E-mail collection service

An e-mail collection service is the functionality of automatically retrieving different e-mail accounts from different e-mail providers. In this way, it is no longer necessary to retrieve e-mails from each individual e-mail provider and all e-mail accounts can be managed via a central collection point.

E-mail signature

An e-mail signature contains more detailed information about the sender and is typically found at the end of an e-mail message.

Since 01.01.2007, merchants within the meaning of the German Commercial Code (HGB) and their employees are required by law to create an e-mail signature with at least the following elements:

  • Surname, first name of the sender
  • Name, registered office and legal form of the company
  • First and last names of managing directors and supervisory board chairmen
  • Commercial register number and competent register court
  • Value added tax identification number

The legal basis for e-mail signatures are paragraphs 37a of the German Commercial Code (HGB), 35a of the German Limited Liability Companies Act (GmbHG) and 80 of the German Stock Corporation Act (AktG).

Telephone number, fax number, e-mail address and website are not further regulated in the legal texts and are therefore not mandatory information. However, this information has proven helpful in practice for recipients of e-mails and is therefore now an integral part of e-mail signatures.

HTML mails

In contrast to a plain text mail, HTML mails can contain different font sizes, font types and colours. HTML mails were not originally intended for use in e-mails. Therefore, in the past, there were security gaps that caused e-mail worms to spread and the recipient to unintentionally disclose information such as tracking pixels. However, these problems have improved considerably. Nevertheless, HTML mails have the reputation of being more insecure than pure text mails.


SMTP is an Internet protocol and stands for Simple Mail Transfer Protocol. SMTP is used in particular for sending or forwarding e-mails, i.e. for sending e-mails.


POP 3 (Post Office Protocol) is an Internet protocol. Using POP 3, it is possible to retrieve e-mails from a mail server. If there is a connection to the Internet, e-mails are retrieved, stored on the local workstation and usually deleted from the mail server. This is the typical process. Meanwhile, most e-mail services offer the option of keeping e-mails on the mail server.

A permanent internet connection is not necessary with POP 3. The e-mail client connects to the e-mail server when needed and retrieves the e-mails, which can then be processed offline.

Typical e-mail clients that support POP 3 are Outlook Express, Apple Mail or Mozilla Thunderbird.

POP 3 provides read access to e-mails. Sending e-mails is controlled by other Internet protocols (e.g. SMTP).

If you are faced with the decision between IMAP 4 or POP 3, IMAP is recommended. In addition to the functionalities available with POP 3, IMAP 4 offers bidirectional communication between the mail server and the e-mail client.


IMAP 4 (Internet Message Access Protocol) is an Internet protocol that allows access to and management of e-mails. In contrast to POP 3, the e-mails remain on the mail server with IMAP 4. This means that even when several e-mail clients are used, the current status including the folder structure is always displayed. Local storage of data is therefore obsolete and increases security against potentially dangerous e-mails, as they can be deleted directly on the mail server. To protect mailboxes or data from third parties, the connection from the mail server to the e-mail client can be encrypted via SSL/TLS. However, this must usually be activated both in the e-mail client and on the mail server.

Typical mail clients that support IMAP 4 are Outlook Express, Apple Mail or Mozilla Thunderbird. Changes made in the e-mail client (e.g. moving an e-mail to a folder) are taken into account on the mail server and thus on all other e-mail clients used. This is called bidirectional communication between the mail server and the e-mail client.

IMAP provides access to e-mails. The sending of e-mails is controlled via other Internet protocols (e.g. SMTP).

Mail User Agent (E-mail client)

Mail user agents or e-mail clients are used to read, compose, send and receive e-mails. An e-mail client can download e-mails from a mail server using POP 3 or open them directly on the mail server using IMAP 4. To send e-mails, the e-mail client sends the e-mails to a mail transfer agent, which is typically an SMTP server.

To set up an e-mail client, you need the names of the SMTP and POP 3 or IMAP servers (also called incoming or outgoing mail servers). In addition, a user name and password are required.

Mailing lists

Typically, e-mails are exchanged between two participants. But sometimes it makes sense to reach several people at the same time. The limits of a webmail service or even an e-mail client are quickly exhausted when dealing with a really large number of recipients. In addition, when all recipients collaborate, care must always be taken to ensure that the replies are also sent to all participants.

Typically, e-mails are exchanged between two participants. But sometimes it makes sense to reach several people at the same time. The limits of a webmail service or even an e-mail client are quickly exhausted when dealing with a really large number of recipients. In addition, when all recipients collaborate, care must always be taken to ensure that the replies are also sent to all participants.

The list server offers the advantage of writing to only one e-mail address in order to reach all list members. The addresses of the individual list members remain hidden and thus protected. Recipients can also subscribe or unsubscribe themselves via the list server's user interface if the list administrator wishes to do so.

Push e-mail

Push e-mail describes a process in which incoming e-mails are directly and immediately forwarded from the mail server to e-mail clients. As soon as a new e-mail arrives on the mail server, a connection is established from the mail server to the e-mail client.

In contrast, e-mails are "fetched" from the mail server during "e-mail polling". Depending on the configuration, this happens at login, at predefined time intervals and when the user manually requests it.

Push e-mail is particularly important for mobile devices. Especially when it comes to receiving e-mails without delays, without the recipient having to manually activate the e-mail retrieval.

Receiving e-mails immediately on the e-mail client is also possible with IMAP idle. With IMAP idle, a permanent connection is maintained between the e-mail client and the mail server. However, this procedure is disadvantageous for mobile phone tariffs that charge on a per-minute basis.


SSL (Secure Sockets Layer) and its successor TLS (Transport Layer Security) are encryption protocols for the secure transfer of data on the World Wide Web.

An encryption protocol makes it possible that third party users cannot view, save or change sensitive data such as bank data during transmission on the internet. As a user, you can recognise that the SSL or TLS encryption protocol has been triggered by the abbreviation HTTPS in the URL or by a closed padlock. If you call up an HTTPS page, the browser used checks whether the operator of this website uses a valid security certificate. This certificate, together with the address of the server, is checked with the certification authority for validity and affiliation. If the data meet all criteria, the computers communicate via symmetric key. This communication takes place on the basis of asymmetric encryption procedures and is therefore secure. This procedure guarantees communication with the website operator and eliminates the possibility of third parties reading and manipulating the data. Increased security goes hand in hand with increased demand for computing power. Therefore, many website operators decide to encrypt only those pages via SSL that require sensitive user data.

In online banking and online shopping, special attention should be paid to increased security standards. SSL versions with version number 3 or higher should be used there. Caution is advisable with version numbers below 2, as these versions could be outdated and error-prone. As far as encryption is concerned, encryption from 112 bit (IDEA encryption) is considered secure.

Webmail service

With a webmail service, you can access e-mails from any computer connected to the Internet. In contrast to e-mail clients, webmail services are computer-independent. While e-mail clients can only be used to access e-mails from computers on which the individually configured e-mail client is installed, e-mails can be accessed from anywhere via webmail services, provided the computers used for this purpose are connected to the Internet.

Once an account has been set up with one of these webmail services, it is sufficient to navigate to the homepage of the webmail service, authenticate oneself by means of a user name and password, and the individual e-mail box can be administered.

There are currently a large number of webmail services on offer. However, the differences are considerable. When choosing a suitable webmail service, the following aspects should be taken into account:

  • Spam protection
  • storage space
  • maximum size of attachments when receiving and sending
  • user-friendliness
  • virus protection
  • range of additional communication media such as SMS, fax or answering machine
  • IMAP 4
  • e-mail collection service
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