Even if the messages are end to end encrypted I wouldn't trust a third party with that data (unless it was a company that does it for a living.)
I'd probably recommend running your own instance, I imagine for that few users it would be pretty cheap. Though maintenance is probably the biggest issue there.
Or just use a third party Matrix server but send client info over email using GPG keys. That would cost you nothing.
Thank you. I think in my (ill-educated, poorly framed) original question, I think I was seeing if there were recommendations from the list on joinmatrix.org/servers/ I see that some are green-lit for privacy while others aren't.
This team isn't enterprise level or anything and I'm just looking to elevate them from emails to, originally, Slack. They're not sharing state secrets or anything, but are inconsistent about sharing client information that while not necessarily directly identifiable, should be kept under a tighter lid than it currently is.