> What does happen when receiving a new MMS of 'n' contacts who are not in your Agenda? We are going to use `createThreadMockup`, and there we are not requesting `findByPhoneNumber`, so when tapping on this thread, the info will be ready?

There is no way that a `messagereceived` event (for a this new thread) will be dispatched before a `messagesending` event. `MessageManager.getThreads(ThreadListUI.renderThreads);` is called from `MessageManager.onMessageSending`, long before `MessageManager.onMessageReceived`, and this is the only place `createThreadMockup` is called. 

> Are we going to render the headers properly? Furthermore, if the request to Gecko (due to is async.) takes 10 seconds (it's only a exaggeration, but it's for trying to explain my doubt here) and meanwhile you have entered into the thread, When are we going to update the headers? Because https://github.com/mozilla-b2g/gaia/pull/10254/files#L6R992 seems not to be ready for this type of things.

We can cache contact/recipient that is selected from the contacts suggestion—I'll try this.