Two basic incoming e-mail servers are in common use today. These servers correspond to the two major incoming e-mail protocols: POP3 and IMAP4. In Red Hat Linux, both servers are available as part of the imap-* RPM package, and are installed as an xinetd service (see Chapter 23 ).
You don t need to create your own e-mail server. You can set up yourself or your clients to use an e-mail server from a provider such as mail.com or yahoo.com . If you want to create your own e-mail server, install the imap-* RPM. Remember to activate its xinetd configuration with the service servername on command, and then run service xinetd reload to make sure xinetd rereads the appropriate configuration file.
If you have a DNS server on your LAN, you can also configure it with an MX entry in the appropriate /var/named database file. For more information on DNS, see Chapter 24 .
The POP3 protocol is still more popular on the Internet. When you connect from an e-mail client, a POP3 server automatically downloads your e-mail. With most clients, you can choose to keep an original copy of the e-mail on the server.
In contrast, the IMAP4 protocol is more flexible. If you re using an IMAP4 server, you can organize your e-mail on folders on the server. You can search through different messages for keywords, and you can download the messages you want. This is useful for users with multiple computers who need a central database for their e-mail.
Once you ve activated a POP3 server, you ll need to create accounts. Anyone who wants to use your POP3 server will require an account on your system. However, those users do not need a home directory.
As you might recall from Chapter 09 , the useradd username command automatically creates a home directory for a new user. However, if you add a new user by directly editing /etc/passwd , you don t have to add a home directory. Then the passwd username command allows you to assign a new password.
Once you ve created a user account, you ll need to tell your user to add the username and the FQDN of the computer that you ve configured as the e-mail server to his or her e-mail client. The latter part of this chapter includes details on how to do so with various e-mail clients.
After you ve activated an IMAP4 server, you ll need to create accounts (the same as you would with a POP3 server). If somebody wants to use your IMAP4 server, that person will need an account on your system. Unlike for a POP3 server, users on an IMAP4 server do need home directories on your system.
The useradd username command automatically creates a home directory for a new user, as detailed in Chapter 09 . Then the passwd username command allows you to assign a new password.
When you ve created the account, as you would with the POP3 server, you ll need to tell your user to add the username and the FQDN of the computer that you ve configured as the e-mail server to his or her e-mail client.