I did try that out at least like five years ago. It's not actively developed anymore, but the premise was E2EE messaging like email but with cryptographic identities similar to nostr.

Messages were broadcasted among peers similar to bitcoin in hopes that your recipient was connected to those peers across a few hops.

When I used it, messages were delivered 90% of the time but it was an interesting project far before nostr came along or messaging apps tried to mitigate metadata leakage and become decentralized.