You can access cPanel and Webmail behind a tight firewall or your company's restrictive firewall using the script from the link below:

http://cpanelproxy.net

IMPORTANT:
Installation requires that you have access to cPanel, so you need to
use a system that isn't behind a firewall to install it initially.

There are instructions embedded in the php file, but here's what you can do to get it working.

1) Load up cPanel (www.yourdomain.com/cpanel or www.yourdomain.com:2085)
2) Add a subdomain called cpanel.
3) Copy the script cpanelproxy.php to the /public_html/cpanel/ directory.
4) Modify (or add) the file /public_html/cpanel/.htaccess to include
the following 3 lines:

RewriteEngine on
RewriteCond %{REQUEST_URI} !^/cpanelproxy.php
RewriteRule .* /cpanelproxy.php [last]

That's it. Once your subdomain is available, you can use
http://cpanel.yourdomain.com to get into cPanel and Webmail.

Please note that fastwebhost.com does not guarantee that this script will work.

Good Luck!