There are servers that send e-mail, and servers that receive e-mail. Modern versions use some basic TCP/IP protocols: SMTP, POP3, and IMAP4. To send and receive e-mail through these protocols, you can choose among three types of mail services: MTA, MDA, and MUA. An MTA such as sendmail sends e-mail through a network. An MDA such as procmail takes messages from the Internet and stores them in spools, sometimes on incoming e-mail servers. An MUA is an e-mail client such as pine , KMail, Mozilla Mail, or Evolution.
sendmail is currently the most popular outgoing e-mail server on the Internet. Since editing the sendmail.cf configuration file is difficult, Red Hat provides a macro file, sendmail.mc , which can be more easily understood and edited. It is easy to convert into sendmail.cf with the m4 macro processor. There are other important sendmail configuration files, including /etc/sysconfig/sendmail and /etc/aliases , as well as other files in the /etc/mail directory. Once you have your new sendmail.cf file, you can make the sendmail daemon reread it with the service sendmail restart command.
There are two basic options for e-mail servers that conform to the POP3 and IMAP4 protocols. Secure versions of each server are available. All are xinetd services that can be installed from the imap-* RPM package. Once these services are installed and activated, your users will need a username and the FQDN of the e-mail server. If it s an IMAP4 server, they ll also need a home directory for their e-mail files.
Both text and graphical e-mail clients are available. One useful highly configurable text-based client is pine . Graphical e-mail clients are available in a number of forms, including Evolution, Mozilla Mail, and KMail.
In the next chapter , we ll take a look at various FTP clients and servers. The FTP client is flexible; you can even use FTP commands to connect and upgrade your RPMs. You can install anonymous, standard, and even secure FTP servers on your Red Hat Linux computer.