As an private channel owner I would like my messages to stay safe

[KrzysztofMadejski]

Ideally it would be great if multi-slack could not read messages shared between private channels. This way trust for server admin wouldn't be an issue. If there is a possibility it would be cool to symmetrically encrypt such communication using secret keys known only to participating parties. That though raises a problem if some new organization would be added.

A softer solution would be not to keep such messages on multi-slack server; just get them, distribute and forget.