Go to http://gx5.co.uk:8443 and login
When logged-in, click on the mail tab.
Then choose the account you want to manage.
After that, select the "Forwarding" tab.
Then tick the box that stats "Switch on mail forwarding".
Then you simply add by typing in the email address you wish to forward to.
You can type each address on a new line, or separate addresses with white spaces, commas, and semicolons.