You want to read mail on a POP or IMAP mail server securely, using Evolution. The mail server supports SSL.
In the Evolution menu Tools/Mail Settings/Edit/Receiving Mail, check "Use secure connection (SSL)".
The default ports for IMAP and POP over SSL are 993 and 995, respectively. If your server uses a non-standard port, specify it.
If you're having problems establishing the connection, you can test it. [Recipe 8.10]
Evolution on Red Hat 8.0 does not appear to check any pre-installed trusted certificates automatically. As it encounters certificates, it will store them in ~/evolution/cert7.db. This file is not ASCII text, so adding certificates is not easy; you'll need the program certutil.
certutil is found at http://www.mozilla.org/projects/security/pki/nss/tools/certutil.html. Additional discussion is found at http://lists.ximian.com/archives/public/evolution/2001-November/014351.html.