I couldn't think of a use case for something this. For anyone else like me, the readme outlines one near the bottom which seems genuinely nice:
Set this up, allow no-auth sending from any address on your LAN, and then spinning up new local services that need outgoing mail is easy, because you can just give them the IP of the relay and omit credentials.
I am constantly surprised how seldom aider is mentioned in threads like this. I understand that it's not directly integrated into the editor, but the "editor + parallel CLI tool chain" paradigm feels so natural to me because we drop to terminal for so many other parts of building software. If you haven't tried it (particularly the architect/editor modality), it's worth a couple of hours of experimenting.
Set this up, allow no-auth sending from any address on your LAN, and then spinning up new local services that need outgoing mail is easy, because you can just give them the IP of the relay and omit credentials.