This whole industry is meant to harvest user information. Richard Stallman tried to warn us. Jaron Lanier called it "siren servers", because they hypnotized people into using their services. I hope this encourages people to question this and and to look for alternatives.
> but if they "actually delete it"--which I imagine you want--then they might also forget any unique identifier stored with the message, which likely makes it hard to know that this message was both already received and deleted in the past.
I would expect any messaging app to work like email, where you're also in control of the email server. Once you receive someone else's message, it's in your inbox, and you can delete it forever as well. The email message model is more intuitive, and I would love for modern instant messaging clients to work the same way except in real time. Of course when you have that level of control, you would need to make it paywalled or subscription of some kind.
