I found an interesting side-effect of the Juniper firewalls when you introduce IPv6. In hindsight it appears perfectly reasonable but if you are not aware of it in the first place you may have a much more permissive firewall than you thought. My setup is such that my internet address changes every time I connect to an ISP. I have services “behind” the Juniper that I want to expose onto the Internet, in this case a mailserver.