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Mail Servers
{MAJOROS} offers many advanced applications to serve and access email. This chapter describes modern email protocols in use today, and some of the programs designed to send and receive email.
Email Protocols
indexterm:[email,protocols] Today, email is delivered using a client/server architecture. An email message is created using a mail client program. This program then sends the message to a server. The server then forwards the message to the recipient's email server, where the message is then supplied to the recipient's email client.
To enable this process, a variety of standard network protocols allow different machines, often running different operating systems and using different email programs, to send and receive email.
The following protocols discussed are the most commonly used in the transfer of email.
Mail Transport Protocols
Mail delivery from a client application to the server, and from an originating server to the destination server, is handled by the _Simple Mail Transfer Protocol_ (_SMTP_).
indexterm:[email,protocols,SMTP] The primary purpose of SMTP is to transfer email between mail servers. However, it is critical for email clients as well. To send email, the client sends the message to an outgoing mail server, which in turn contacts the destination mail server for delivery. For this reason, it is necessary to specify an SMTP server when configuring an email client.
Under {MAJOROS}, a user can configure an SMTP server on the local machine to handle mail delivery. However, it is also possible to configure remote SMTP servers for outgoing mail.
One important point to make about the SMTP protocol is that it does not require authentication. This allows anyone on the Internet to send email to anyone else or even to large groups of people. It is this characteristic of SMTP that makes junk email or _spam_ possible. Imposing relay restrictions limits random users on the Internet from sending email through your SMTP server, to other servers on the internet. Servers that do not impose such restrictions are called _open relay_ servers.
{MAJOROS} provides the Postfix and Sendmail SMTP programs.
Mail Access Protocols
There are two primary protocols used by email client applications to retrieve email from mail servers: the _Post Office Protocol_ (_POP_) and the _Internet Message Access Protocol_ (_IMAP_).
indexterm:[email,protocols,POP] The default POP server under {MAJOROS} is [application]*Dovecot* and is provided by the [package]*dovecot* package.
Installing the dovecot package
In order to use [application]*Dovecot*, first ensure the [package]*dovecot* package is installed on your system by running, as `root`:
~]#{nbsp}dnf install dovecot