Great question! Think of it this way: your own machine acts as the server. So yes, in your scenario, the message waits on your machine until both sides are online at the same time. Once that happens, it gets delivered automatically. It works exactly like regular email, except your PC does the job instead of an external server. No middleman needed. In practice, if you leave PeerBox running, the overlap happens naturally, even for a few seconds. And if you really need guaranteed async delivery across very different time zones, you could just keep PeerBox running on a machine that stays on, like a small home server or a Raspberry Pi.

PeerBox was designed to offer the highest level of privacy possible by cutting out every middleman. That does come with a little less flexibility than regular email, but you have several options. You can install it on a Raspberry Pi or any small machine that stays on, which gives you near-permanent availability. You can also simply agree on a time window with your contacts for message exchange. And actually, we're considering releasing a VPS-compatible version soon, which would do exactly what you're describing. Stay tuned!