Feature request: Executables/pipes as transports, BSMTP?

[Mihara]

At least I think this is a feature request, the documentation is not very clear...

Assume I'm using NNCP which is a poorly documented but powerful way to set up highly encrypted friend-to-friend delay tolerant networks, named after UUCP and mimicking it in functionality in several respects. One of its intended uses is serving as an email transport, so one can package email for delivery and pass it through NNCP to where it needs to go.

The way to do that with Postfix and Exim is known. The only kind of transports mox appears to support are SMTP to a specific host ("smarthost"), a SOCKS proxy, and direct connection. At least, nothing else is obviously described and I don't see anything else with a quick skim through the source.

There is no way to imitate the Postfix or Exim setup described above that I can see.

1. Is this reasonably practical to implement at all, with the way mox's security works? I remember the fairly arcane (for me) systemd settings basically jailing the server process, so I wouldn't be too surprised if it's not feasible.
2. Perhaps there's a separate "buffer" localhost-smtp solution somewhere, that mox could communicate with that wouldn't be restricted from running arbitrarily chosen executables? E.g. I run something very simple on a separate port that only listens to mox, mox uses it as a transport, it does the back and forth with NNCP?

[mjl-]

Your analysis looks correct. Mox can't run commands for outgoing deliveries.
For security, I think it's a worthy goal to never execute any external
commands. I haven't heard of other reasons to execute commands to deliver
messages.

Using a separate tool that accepts a message over smtp/submission and runs a
command seems like a good solution. A tool like that likely already exists.
Otherwise it should be easy to write.

[Mihara]

Otherwise it should be easy to write.

After some meditation on the subject, I realized that for the whole scheme to work, it must be possible to configure Mox to ignore DKIM and every other kind of protection for messages matching something. I.e. at least this proxy tool itself must be exempt from all checks to deliver mail from the NNCP side of the equation. And likely, hosts on the other end of this network must also be exempted somehow.

Is this currently possible with Mox at all?

[mjl-]

Is this currently possible with Mox at all?

You can deliver a message to any address with mox deliver $address < message.eml. You would have to run it as the mox user.