John-- I hope I have not been too much of an alarmist. There is a big difference between "a group free of tracking, status reports, friend requests, adverts and general intrusion" and the kind of privacy that protecting health records from prying employers, journalists conversing with vulnerable sources,or other high profile situations require. Groups.io serves well for the first kind of privacy, but any service that uses email has the privacy level of postcards. Postcards are public, but not conspicuously, and it takes considerable effort to exploit them. Emails can be subpoenaed, bad actors sometimes get to them, security breaches occur.? And any service depends on the honesty and integrity of its operators who must show a profit.
Groups.io does not exploit the messages on its servers in any way that I can see, which is one of the reasons I am an enthusiastic supporter of Groups.io. Many free services exploit the data on their systems for revenue. This is a good reason to upgrade to paid premium service or donate to Groups.io. The lights won't stay on at Groups.io if the bills aren't paid.
If you are emphasizing privacy to your group, I might mention to them that email is not private, and suggest that members review the terms of service of their email provider. I use Gmail myself, with the knowledge that Google is scanning my email just like they scan my Google searches. I simply accept it as the price of Gmail's convenience. I haven't looked at the Oath: (Yahoo) terms of service, but when Verizon acquired Yahoo and AOL, they told their shareholders that they intended to use Yahoo and AOL to build ad revenues and Google's efforts their have been successful.
I may be more cynical than Shal. I've seen egregious conduct in business when big bucks are on the table and the lawyers say the TOS protects them.
Best, Marv
Marvin Waschke