Which level is used for emails


E-mail is the abbreviation for electronic mail, which means "electronic mail" or "electronic letter". E-mails are created, sent and displayed exclusively in electronic or digital form. In addition to the telephone and messaging, e-mail is a central means of communication in our society. Messages, discussions and exchanges of documents are all possible with email.

Editing of e-mails by the user takes place on an electronic device with Internet access. After sending, the e-mail is sent within a network or over the Internet. For the recipient, the e-mail is displayed again on an electronic device with Internet access. Sending, receiving, reading and writing of e-mails is done with the appropriate software or in a browser, in which a graphical user interface for managing e-mails is shown.

In 1971 an e-mail was transmitted between two computers in what was then the ARPANET for the first time. Afterwards, e-mails were exchanged between university staff on a scientific level. In the course of the commercial use of the Internet, e-mail established itself as a means of communication in private and business environments. E-mail replaces or supplements telephone, fax and letter with a quick way of digitally transferring messages and documents. Nowadays, electronic mail has become indispensable and has partly replaced letters and faxes as fast and direct communication.

E-mail address

As with the letter, every e-mail must be given an address for the recipient. The e-mail address is identified by the unusual character "@" (spider monkey). It is used as a separator between the user name and the domain name (server address). This is where the e-mail address differs from other Internet or network addresses.

Process of e-mail communication with outgoing and incoming mail

E-mail communication takes place via a client and a server. A distinction is made here between the incoming mail server and the outgoing mail server, which can be different servers. Communication between clients and servers is based on the client-server principle.

The distinction between incoming and outgoing mail is because when it comes to e-mail, it is assumed that the user is not always online. For example, because the PC is switched off or because Internet access is established via dial-up access and then there is only a temporary connection. So if the recipient of an e-mail is not online, then you cannot send him an e-mail. In order for this to work anyway, two intermediate steps are required. Once the sending of e-mails via the outgoing mail server. And receiving and saving e-mails via the incoming mail server. Communication takes place using the SMTP, POP and IMAP protocols.

  • MUA - Mail User Agent (email client)
  • MTA - Mail Transfer Agent or Message Transport Agent (outgoing mail server)
  • MDA - Mail Delivery Agent (incoming mail server)

When sending an e-mail, the sending e-mail client (Mail User Agent, MUA) sends the e-mail to its outgoing mail server (Mail Transfer Agent or Message Transport Agent, MTA) via SMTP. From there, the email is forwarded to the recipient's MTA via SMTP. Since this server cannot send the e-mail to the recipient on its own, it moves the e-mails to the incoming mail server (Mail Delivery Agent, MDA). From there, the receiving e-mail client (Mail User Agent, MUA) must pick up the e-mails via POP or IMAP.

What does the DNS server do? Because an email address does not contain the domain name of the recipient's mail server, the mail server address is stored in the MX record of the (authoritative) DNS server and can be queried by DNS request.

SMTP - Simple Mail Transfer Protocol

The SMTP protocol is responsible for the transmission of e-mails from the sender's SMTP client to the SMTP server (outgoing mail) and from there to the recipient's SMTP server. To do this, the sender's e-mail client contacts its own SMTP server (outgoing mail server) and hands over the e-mails that are waiting to be sent.

POP - Post Office Protocol

Since e-mail users are usually not always online in order to always be able to receive e-mails, all incoming messages are cached. To pick up the e-mails, the recipient contacts his incoming mail server with POP.
POP is not suitable for access from multiple devices to an e-mail inbox because it can load and delete e-mails from the inbox. POP does not know how to manage e-mails (move, copy, delete) in folder structures. In addition, the client cannot maintain the connection to the server (idle function) in order to "push" new incoming mails to the client. This is only possible with IMAP.

IMAP - Internet Message Access Protocol

In principle, IMAP has the same task as POP. However, it offers several advantages. IMAP defines methods for creating, deleting and renaming a mailbox and for checking whether new messages have arrived. IMAP also allows partial loading of an e-mail and directory services within the mailbox.
In contrast to POP, users can choose which emails they want to download for reading. This is an advantage especially when using a connection with a low bandwidth.


E-mails are usually downloaded from the incoming mail server using POP and then deleted on the server. This means that POP is suitable for offline processing of e-mails in times of Internet access via dial-up lines. But in the age of "always-on", this approach is anything but practical. It would be advisable to leave the e-mails on the server and only download the e-mails that you want to read. POP is also unsuitable if you want to access a mailbox from different computers and devices. Everywhere you then have a different data status. The emails are scattered everywhere.

But there is the IMAP protocol. This protocol works in online mode and can also create folders on the e-mail server in order to save and archive the e-mails there. If you have enough storage space you can categorize and archive the emails there over several years. E-mails with IMAP also have different labels. For example "deleted" or "read". Regardless of the client, you have access to your email inventory, just as if it were stored locally.
IMAP works on an interactive client-server model in which messages remain on the server until they are permanently deleted. So you always have access to e-mails from different devices as soon as you are online.

POP is an old protocol and no longer corresponds to the modern handling of data. With POP, e-mails have to be saved locally. And yet IMAP has not really caught on. Many private email users prefer to use webmail
The only drawback is the storage space for IMAP, which must be available on the e-mail server. This is of course not always desirable for Internet providers, although every provider supports IMAP. Most of the time, you can choose to access the mailboxes via POP or IMAP without having to configure it on the provider side. All common e-mail clients also support IMAP for access to e-mail mailboxes.

Spamming, phishing, pharming

E-mail in itself would be a perfect means of communication if it weren't for the constant attempts at abuse by criminals. Advertising e-mails are sent en masse and the e-mail addresses of strangers are also misused. In addition, phishing and pharming are used to ask people who are inexperienced to enter access data for online banking accounts in almost perfectly imitation websites in order to empty accounts afterwards.
Although large parts of society have now been informed about such machinations, people repeatedly fall for attempted fraud.
For these reasons, no e-mail account can do without a spam filter and antivirus function.

De-Mail: Legally secure e-mail (in Germany)

De-Mail is an electronic form of communication based on e-mail that can be used for legally binding and confidential communication with authorities, companies and customers. De-Mail users can send and receive De-Mails just as quickly and easily as e-mails.

How secure is email? (Secure email)

When the protocols and programs for e-mail were developed, IT security and anonymity were not an issue. Email works like a postcard. The content of an e-mail is not protected from the eyes of others. The content of an email can be manipulated unnoticed. The sender of an email does not necessarily have to be correct.

Various methods have been developed to make e-mail more secure. However, they are all optional. You can, but don't have to, use it. As a result, email is usually always insecure. This means that the content and origin of an e-mail cannot be proven or determined with absolute certainty. The sender and content of an email can be manipulated.

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