Yea, it seems like this is the most information they could give you without violating the addressee's privacy by revealing whether they have uninstalled the app. I suppose it could be worth it if, when the message remains undelivered for a while, Signal added an explicit note to that effect so the sender doesn't misunderstand.

Yes, exactly this. All that's needed is to tell senders when a message wasn't received after X hours.

You don't have to figure out if the user uninstalled. This also happens if they get a new phone and don't re-install on it, so relying on uninstalls wouldn't work anyway.

How can they tell that a user has uninstalled the app? Does uninstalling send a notification to signal.org?

Uninstalling doesn't send a notification to signal.org, I've previously messaged a few people without getting a response, later realizing they never got it because they switched phones and stopped using Signal without pressing the "Delete Account" button in Signal settings. The workaround is to have the user install+register again, then press delete.

https://support.signal.org/hc/en-us/articles/360007061192-De...

> Signal must be actively working on your phone to make changes to the account. Register to see these options for your number. Deletion requests are not accepted outside of the registered app because there is no way to accurately verify whether or not a number is truly associated with the requester.

Yes, I expected as much: most users who stop using Signal (because, say, their friends use something else) are more likely to either just stop using it or uninstall the app, without explicitly deleting the account.

FCM system they use to deliver notifications will return the delivery ID as no longer valid after uninstall though.

I dunno. It's true they might not even have that information.