They’ve stated that they are using Mac minis as relays. They claim that they do not store messages or credentials, but I don’t see how that’s possible if it relies on a Mac or iOS relay server that they control.

The best they can do is pinkie-promise to not intercept your messages and send a copy to law enforcement. But Nothing Corp can only guarantee… Nothing.

And yet, this article acts as if you’re using end-to-end encryption:

messaging Android users will use encrypted RCS chats, while messaging iPhone users will use encrypted iMessage chats.

They might be able to relay them in a way that the end to end encryption is actually handled on the phone and the relay only relays encrypted messages.

That would likely still give them a capability to MitM but it’s plausible that they couldn’t passively intercept the messages.

On second thought… Wouldn’t they have to reverse engineer at least part of the application, and at that point, would they even need Macs?

Absolutely. The iMessage network isn’t some unknowable beast, it “just” requires an Apple device be involved and activated to work. In order to spoof that far, you’d essentially need to emulate quite a bit on device.