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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.