@Wat-now my proposed configuration might work but is possibly incorrect. The debian configuration is not really theirs, it's simply the default upstream source configuration. Arch removed by purpose the allow send_destination line (that I reintroduced) from the root policy block and replaced the policy at_console block with a network group policy, the latter containing the allow send_interface line. So it's not that straightforward as it seemed and the changes that I made might not really make sense. I even tried the default source configuration but it didn't work, so far the only working configuration is the one that I posted before...
