ESET MAIL SECURITY Installation Manual page 16

This chapter describes integration of the ESET Mail Security with the variety of known e-mail
messaging systems. Knowledge of e-mail messaging system basic principles (figure 5-1) is of
paramount importance for understanding of ESETS operation.
Figure 5-1. Scheme of UNIX OS e-mail messaging system.
MTA - Mail Transport Agent
A program (for instance sendmail, postfix, qmail, exim, etc.) providing e-mail messages
transfer among local and remote domains.
MDA - Mail Delivery Agent
A program (for instance maildrop, procmail, deliver, local.mail, etc.) providing delivery of
locally addressed e-mail messages into particular mailboxes.
MUA - Mail User Agent
A program (for instance MS Outlook, Mozilla Mail, Eudora, etc.) providing access and
management of e-mail messages, i.e. reading, composing, printing etc., stored in mailboxes.
MAILBOX
A file or a file structure on a disk serving as the storage space for e-mail messages. Note that
there are several formats of MAILBOX in Linux/BSD/Solaris OS: an old fashioned format where
e-mails for each user are stored sequentially in one user appropriate file located in directory '/
var/spool/mail'; MBOX (a bit newer but still an old format) with e-mails stored sequentially in one
file located within user home directory; MAILDIR with e-mails stored in a separate files within a
hierarchical directory structure.
The e-mail server receives data communication typically using SMTP - Simple Mail Transfer
Protocol communication. The received message is transferred by MTA either to another remote
e-mail messaging system or it is delivered using local MDA into particular MAILBOX (we assume
each local network user owns a MAILBOX located at the server disk). Note that it is responsibility
of the user's local MUA to provide download and correct interpretation of the message at the
user's computer. When retrieving data from MAILBOX the MUA uses typically POP3 - Post Office
16
INTERNET
smtp
S1 MTA
S3
E-Mail 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