> The downside is that they will opportunistically send your messages via Signal. If the recipient chooses to not have SIgnal installed any longer, then your messages go into a black hole.

The user cannot just log out of Signal and have the app on other people's devices automatically fall back on SMS the way it works with iMessage?

A lot of people will just delete an app and think there were no side-effects. There was an article here a few weeks ago about people not cancelling in-app subscriptions after deleting an app. Apple will remind you after it deletes it, Google does not.

Logging out might not even be enough, depending on the logic on Signal’s side. Do they use active devices, or just that an account exists?

Apple has the same problem, and an article and entire process for disabling it out of band, plus a heartbeat so it’s done automatically after a while if you don’t reset your phone. It’s a major problem.

I’ve only done the switch from iOS to Android once and I remember it was a pain for a few days until everything realized I didn’t have iMessage anymore.

Even without an iPhone I sometimes miss texts from people using iMessage because my only occasionally used MacBook seems to randomly like to turn messages back on, and so anything from an Apple user ends up there instead of on my phone. It stays that way until I figure out I’m missing texts and go find them on the MacBook and have to manually turn off messages to it again.

> If the recipient chooses to not have SIgnal installed any longer, then your messages go into a black hole.

For two weeks, messages will be shown as sent but not delivered, and after two weeks Signal will not let you send messages to that number until it reconnects to the Signal servers.

For comparison, Apple automatically sends all SMS messages via iMessage opportunistically, and if the user then switches to another phone, all SMS messages from iOS users will be silently discarded in perpetuity. This is a big problem because the recipient has no idea that they're missing messages, and also if they no longer have access to an iPhone, there's no way for them to deregister their phone number from iMessage.

That hasn't been true for awhile:

https://selfsolve.apple.com/deregister-imessage/

They will also deregister you automatically after some period of time. What you described is the situation several years ago, but it's much better now.

That's a link to deregister a phone number from iMessage without an iPhone, which is good, but I don't see any text on that page that confirms that they'll deregister you automatically, or if there's any user-visible indication of the issue. If that's the case, then I'm glad they finally addressed it, because it was definitely a problem for far too long.

In that case, Signal's current behavior would be comparable to Apple's, if Apple also deregisters you after a period of inactivity.