The main way I specialize messages at this point is basically 'Am I going to want this later'? If the answer is yes, I use email. If not I use Signal. It's interesting this was the most requested feature... it wouldn't be for me even though I love Signal.

It's important for Signal groups, because on a new device without a backup the groups you were in don't show up until someone sends a message in the group. Say if you were the only admin in an announcement-only group, no one else can send a message in the group, so that group is now lost to you.

I like this idea, but I don't think I'd ever be able to convince my wife to run that analysis on any particular message before she decides whether to email or to message me on Signal.

so do you email yourself messages/conversations you want to keep?

Also unless everyone use gpg, email isn't very secure nor confidential.

I tend to use notes on my smartphone for information I want to keep that are encrypted and synchronized on my desktop when reaching home. Having said that I often forget to copy a message to a note because it is a manual process and it is sometimes not trivial to anticipate that an info will be important enough in the future that you need it again.

You can imagine even the same person having some conversations they would want to keep and some they wouldn't.