Installation guide

226 Chapter 15. Email
15.6.2. Secure Email Servers
Offering SSL encryption to IMAP and POP users on the email server is almost as easy. Red Hat Linux
also includes the stunnel package, which is an SSL encryption wrapper that wraps around standard,
non-secure network traffic for certain services and prevents interceptors from being able to "sniff" the
communication between client and server.
The stunnel program uses external SSL libraries, such as the OpenSSL libraries included with Red
Hat Linux, to provide strong cryptography and protect your connections. You can apply to a Certificate
Authority (CA) for an SSL certificate, or you can create a self-signed certificate to provide the benefit
of the SSL encrypted communication.
To create a self-signed SSL certificate, change to the /usr/share/ssl/certs/ directory, type the
make stunnel.pem command, and answer the questions. Then, use stunnel to start the mail dae-
mon that you wish to use.
For example, the following command could be used to start the IMAP server included with Red Hat
Linux:
/usr/sbin/stunnel -d 993 -l /usr/sbin/imapd imapd
You should now be able to open an IMAP email client and connect to your email server using SSL
encryption. Of course, you will probably want to go a step further and configure your stunnel-
wrapped IMAP server to automatically start up at the correct runlevels.
For more information about how to use stunnel, read the stunnel man page or refer to the docu-
ments in the /usr/share/doc/stunnel-
version-number directory.
Alternatively, the imap package bundled with Red Hat Linux contains the ability to provide SSL
encryption on its own without stunnel. For secure IMAP connections, create the SSL certificate by
changing to the /usr/share/ssl/certs/ directory and running the make imapd.pem command.
Then, set the imapd service to start at the proper runlevels.
You can also use the ipop3 package bundled with Red Hat Linux to provide SSL encryption on its
own without stunnel.
15.7. Additional Resources
Many users initially find email programs difficult to configure, primarily due to the large number of
options available. Below is a list of additional documentation to help you properly configure your mail
applications.
15.7.1. Installed Documentation
• Information about how to configure Sendmail is included with the sendmail and sendmail-cf
packages.
• /usr/share/doc/sendmail/README.cf — Contains information on m4, file locations for
Sendmail, supported mailers, how to access enhanced features, and more.
• /usr/share/doc/sendmail/README — Contains information on the Sendmail directory
structure, IDENT protocol support, details on directory permissions, and the common problems
these permissions can cause if misconfigured.
In addition, the sendmail and aliases man pages contain helpful information covering various
Sendmail options and the proper configuration of the Sendmail /etc/mail/aliases file, respec-
tively.