[eridius]

Search could be done locally if the client downloads the whole message history. I don't know enough about how Teams works to know if that's actually something a client can do right now, but it should at least be technically possible.

Another alternative is simply running a bot that indexes everything and provides search. You can run the bot in-house so you keep control over your data.

[x0x0]

I think I'm more uncomfortable with the idea of entire message histories walking around on disks of laptops and phones (not to mention that's a giant problem on phones because of storage/horsepower) than I am with the idea of slack being able to read everything...

[eridius]

Well, the clients could just keep indexes rather than the actual history, and then fetch the specific messages as needed when the search is performed.

[matthewcford]

There are better ways to do search, hash keywords then you can just search the hashes