You've lost me. We have three e-mail addresses on our ISP account, and each one is signed on as a FR username. Bill doesn't use his much.
It's like branches on a tree.
My machine is one branch, the other machines are other branches.
But they're all connected to the same trunk, the network and DSL modem.
So posting from my machine would come from the same IP as, say, my sister's machine.