How can I forward spam mail to a specific email address?

With SMTP Proxy this is possible by changing the value of SMTP>Spam>Spam Quarantine to the Email Address you prefer. Then the quarantine will not be made anymore on the harddisk of the firewall but each mail will be forwarded to that Email Address.

Additionally you can send also a notification to the administrator by setting an Email Address in the field "Email used for notification on Spam Alert (Spam Admin)".

With POP3 Proxy this is unfortunately not possible at all.