It appears that sbbsecho will forward netmail between domains

There doesn't seem to be anything preventing sbbsecho from importing a .msg file that will get forwarded on a different domain.

This would allow sending a FidoNet message from the traditional -1/-1 node address to a system that is in multiple domains, and with an INTL line, have it delivered to a non-FidoNet address.

I'm not sure if file attaches get routed as well, but if they do, this allows fairly trivial untraceable attacks on InterBBS leagues assuming routed netmail goes into the secure inbound.