Why are related emails not always threaded automatically?
In rare occurrences, related emails might not be threaded when the sender is using an outdated email app that, contrary to most apps, does not include References when replying. Some apps can thread without References, but Missive cannot at the moment. References are pieces of information hidden within emails that help email apps thread emails together.
You can always merge conversations back together.
We do want to support threading emails with no References eventually.