Now edit /etc/apache2/sites-available/default. The top has to be changed so that it reads:

NameVirtualHost *:80
<VirtualHost *:80>

Edit /etc/apache2/sites-available/https as well, the top of the file should read:

NameVirtualHost *:443
<VirtualHost *:443>
        SSLEngine on
        SSLCertificateFile /etc/apache2/ssl/apache.pem

Edit /etc/squirrelmail/apache.conf It should look like this:

Alias /webmail /usr/share/squirrelmail

<Directory /usr/share/squirrelmail>
  php_flag register_globals off
  Options Indexes FollowSymLinks
  <IfModule mod_dir.c>
    DirectoryIndex index.php
  </IfModule>

  # access to configtest is limited by default to prevent information leak
  <Files configtest.php>
    order deny,allow
    deny from all
    allow from 127.0.0.1
  </Files>
</Directory>
# users will prefer a simple URL like http://webmail.example.com
#<VirtualHost 1.2.3.4>
#  DocumentRoot /usr/share/squirrelmail
#  ServerName webmail.example.com
#</VirtualHost>
# redirect to https when available (thanks omen@descolada.dartmouth.edu)
#
#  Note: There are multiple ways to do this, and which one is suitable for
#  your site's configuration depends. Consult the apache documentation if
#  you're unsure, as this example might not work everywhere.
#
<IfModule mod_rewrite.c>
  <IfModule mod_ssl.c>
    <Location /webmail>
      RewriteEngine on
      RewriteCond %{HTTPS} !^on$ [NC]
      RewriteRule . https://%{HTTP_HOST}%{REQUEST_URI}  [L]
    </Location>
  </IfModule>
</IfModule>