When you access WebMail you should be prompted by a login box where you enter the email address and password of the mailbox that you wish to access, if you're not prompted by a login box then you are more than likely behind a Firewall which is blocking your access to the required port.
If you have access to the Firewall to open ports you need to allow incomming access to TCP Port 2095, once done you should have full access to webmail.
