Linux offers a number of alternative methods for handling incoming and outgoing e-mail. Red Hat Enterprise Linux includes sendmail, Postfix, and Dovecot for this purpose. (Yes, it includes exim and squirrelmail as well, but sendmail, Postfix, and Dovecot are what's listed in the RH300 course outline, and Dovecot is the new default for incoming e-mail.)
Perhaps the most common server for outgoing e-mail is sendmail, which may already be installed on your RHEL system. Once it is installed and configured, you can set up sendmail as your own personal mail server (subject to the limitations of your ISP). RHEL includes the open-source version of sendmail; the commercial version is known as Sendmail (with the capital S). One alternative to sendmail that is installed on RHEL is known as Postfix.
RHEL includes Dovecot for standard incoming e-mail protocols. It's relatively easy to configure these protocols, including POP3 (Post Office Protocol), POP3S (the secure version), IMAP (Internet Message Access Protocol), and IMAPS (the secure version).
As for the RHCE exam, you may have to configure or troubleshoot the e-mail services discussed in this chapter. So as you read this chapter and look through the configuration files and exercises, be willing to experiment. And practice, practice, practice what you learn.