E-Mail

E-mail is a great example of computer based communication. It is almost as old as the Internet.

Here is an example of a mail traffic:

Your mail user agent (e.g. kmail) connects to a mail server via the POP3 or IMAP protocol. The mail server sends you notification about newly arrived e-mails and such.

Now you send an e-mail to bogus@foobar.com. It is first sent from your mail client to your server and from there, it is sent to the recipient's server. The recipient's server is given by the MX record of the recipient's domain. For transfer between the servers, SMTP is used, so both server are MTAs using software like postfix or sendmail.

If your mail server collects your mail from various other servers, it uses an application like fetchmail.