ESET MAIL SECURITY - ANNEXE 209 Installation Manual page 16

This chapter describes the integration of ESET Mail Security with a variety of known email
messaging systems. It is extremely important to understand the basic principles of an email
messaging system (see figure 5-1) and how ESET Mail Security integrates with it.
Figure 5-1. Scheme of UNIX OS email messaging system.
MTA - Mail Transport Agent
A program (e.g., sendmail, postfix, qmail, exim, etc.) that enables the transfer of email
messages between local and remote domains.
MDA - Mail Delivery Agent
A program (e.g., maildrop, procmail, deliver, local.mail, etc.) that enables the delivery of locally
addressed email messages into particular mailboxes.
MUA - Mail User Agent
A program (e.g., Microsoft Outlook, Mozilla Mail, Eudora, etc.) that provides access to and
management of email messages, such as reading, composing, printing, etc.
MAILBOX
A file or file structure on a disk serving as the storage space for email messages.
The email server receives data communication using SMTP (Simple Mail Transfer Protocol)
communication. The received message is transferred by MTA either to another remote email
messaging system or is delivered using local MDA into a particular MAILBOX. In most cases, each
local network user owns a MAILBOX located on the server. Note that it is the responsibility of the
user's local MUA to provide the function of downloading and correctly interpreting the message
at the user's computer. When retrieving data from MAILBOX, the MUA typically uses POP3 (Post
Office Protocol) or IMAP (Internet Message Access Protocol) to communicate with the MTA. The
SMTP protocol is used to send data to the Internet.
The ESETS operating principle is based on data communication interception and scanning at
the various phases of its transfer. The interception locations are marked in figure 5-1 by symbols
16
INTERNET
smtp
S1 MTA
S3
Email Server
smtp
User Agent User Agent
Client Client
Local Network
smtp
S2
pipe
MDA
file
MAILBOX
S4
pop3/imap
User Agent
Client
ESET Mail Security