Mail Access Protocols - Red Hat ENTERPRISE LINUX 4.5.0 Reference Manual

Chapter 11. Email
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. Modern SMTP
servers attempt to minimize this behavior by allowing only known hosts access to the SMTP
server. Those servers that do not impose such restrictions are called open relay servers.
By default, Sendmail (
Enterprise Linux. However, a simpler mail server application called Postfix
( ) is also available.
/usr/sbin/postfix

1.2. 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).
The use of IMAP and POP is configured through
To configure
dovecot
1. Edit
/etc/dovecot.conf
protocols = imap imaps pop3 pop3s
2. Make that change operational for the current session by running the command:
service dovecot restart
3. Make that change operational after the next reboot by running the command:
chkconfig dovecot on
Unlike SMTP, both of these protocols require connecting clients to authenticate using a
username and password. By default, passwords for both protocols are passed over the network
unencrypted.
1.2.1. POP
The default POP server under Red Hat Enterprise Linux is
by the package. When using a POP server, email messages are downloaded by email
dovecot
client applications. By default, most POP email clients are automatically configured to delete the
message on the email server after it has been successfully transferred, however this setting
usually can be changed.
186
/usr/sbin/sendmail
to use POP:
to have the line:
) is the default SMTP program under Red Hat
; by default
dovecot
/usr/sbin/ipop3d
runs only IMAP.
dovecot
and is provided