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Chapter 16.

Email is one of the most widely used services on the Internet. Red Hat Linux offers many ways for

you to utilize email, whether you are a desktop user or a system administrator.

This chapter looks at popular email protocols that are in use today and various programs designed to

accomplish different types of tasks when dealing with email.

16.1. Protocols

Email, like other network services, uses a variety of protocols. These protocols allow different ma-

chines, often running different operating systems and utilizing different email programs, to commu-

nicate with one another and transfer mail so it arrives in the proper place.

The following protocols are those most commonly used to transfer email from system to system.

16.1.1. IMAP

The Internet Message Access Protocol (IMAP) is a method used by email client applications to access

remotely stored messages. When using IMAP, commonly called IMAP4 after the version of the pro-

tocol used, the email messages remain on the remote mail server, where the user can read or delete

them and create, rename, or delete mailboxes to store the email.

In addition, IMAP is fully compatible with important Internet messaging standards, such as the Mul-

tipurpose Internet Mail Extensions (MIME), to allow attachments to be received. Many email clients

that use IMAP can also be conﬁgured to cache a copy of the messages locally, so that you can browse

previously read messages when you are not directly connected to the IMAP server.

IMAP is primarily utilized by users that may access their email using multiple machines, as messages

are stored in a central location and can be accessed by any system with an IMAP mail client and a

connection to the remote IMAP server. Also, users that connect to the Internet or a private network

via a low-bandwidth connection often use IMAP because only the email header information is pulled

off at ﬁrst. This allows them to defer the downloading of messages containing large attachments until

a time when their limited bandwidth is not in use. In the same way, email that the user does not want

can be deleted without viewing the message body, saving the need to even download it through their

network connection.

The Request for Comment (RFC) documents that cover IMAP contain the assorted details and speciﬁcs

about how the protocol is designed to work. RFC-1730 ﬁrst deﬁned the way IMAP is used in version

4, but RFC-2060 discusses the current IMAP implementation used with many IMAP servers, called

version IMAP4rev1.

The imap package in Red Hat Linux allows users to connect to your system and receive their email

using IMAP. Secure IMAP connections are supported through Secure Socket Layer (SSL) technology

built into the imapd daemon, allowing it to use the /usr/share/ssl/certs/imapd.pem certiﬁcate

ﬁle. The stunnel program is not required to provide SSL-encryption for IMAP connections, though

it can be used. See Section 16.6.2 for more information concerning these two encryption options.

Other free, as well as commercial, IMAP clients and servers are available, many of which extend

the IMAP protocol and provide additional functionality. A comprehensive list can be found at

http://www.imap.org/products/longlist.htm.

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Red Hat LINUX 7.2 - OFFICIAL LINUX CUSTOMIZATION GUIDE Guida di Installazione Pagina 201