If the messages are slow to come, those ephemeral keys become less and less ephemeral, and could actually be stolen.
> If your security model relies on this difference then your security model is broken. It’s worth noting that Signal does NOT rely on this difference. It relies on participants being mostly online to permit frequent rekeys and not having to retain old keys indefinitely.
Signal does not depend on TCP being "bidirectional" as lvh said, it depends on participants being mostly online. This has nothing to do with the transport properties of e-mail vs. TCP.
Sure. The world of cryptography software is already muddled by misinformation, poor practices and misguided appeals to authority. We shouldn't need to spread misinformation about technologies such as e-mail to get people to stop using it.