What I do is to redirect non SSL access to SSL;
Code:
<IfModule mod_ssl.c>
<VirtualHost *:80>
ServerName webmail.freelydifferent.com
Redirect / https://webmail.freelydifferent.com
</VirtualHost>
<VirtualHost _default_:443>
ServerAdmin spam_me@freelydifferent.com
ServerName webmail.freelydifferent.com
ServerAlias webmail.freelydifferent.com
DocumentRoot /var/www/webmail
<Directory />
Options FollowSymLinks
AllowOverride None
</Directory>
<Directory /var/www/webmail>
Options Indexes FollowSymLinks MultiViews
AllowOverride None
Order allow,deny
allow from all
</Directory>
etc...
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