Usually people will just hit "Reply-All" and it's OK, but someone might accidentally add an address list to the CCs or BCCs, and the result is horrible.
But what alternatives exist for non-technical people to have an extended async conversation?
All comments and suggestions welcome, and thanks for reading.
Edit:
Adding information about the context here.
Many of the people involved don't have a smart-phone, and certainly couldn't go through the process of linking an app to a laptop/desktop machine. Sometimes it's tough getting them to use email "properly", which is why I have concerns over them using email for confidential conversations in the first place.
They have email, they have browsers, they are almost invariably using laptops or desktops and not phones, and they are technically inexperienced. I'm guessing that anything suitable would have to be browser based, but I'm open to other ideas.
Thanks.
However if the goal is to prevent accidental leaking by using reply-all or adding an email address by mistake, then I think encryption features are nice-to-haves rather than a must-have. It's a very nice to have, but for non-techies and for your specific use case, usability is probably more important at this point.
I would thus recommend either:
* Discord (https://discord.com/), easy group voice chat should you need one
* Slack (https://slack.com/) using a free account, but they limit the number of messages for free accounts. May not be a deal-breaker for you.
* Element (https://element.io/) which was formerly Riot.im, and is encrypted and have more security features vs. the other two. Probably the most secure here.
All of them have their pluses and minuses, but all of them can be opened in a browser and require no smartphone. I suggest you pick one that you feel is easiest for your group to register and use, and provides the feature set that you require.
With regard to Discord, please make sure to read [0] before making any decisions :)
[0] https://cybernews.com/privacy/discord-privacy-tips-that-you-...
Then perhaps the people involved should be encouraged to trim all the old junk from the bottom of their messages... for exactly the reason you have described.
A discussion between 15 people is inevitably going to get leaked to some extent no matter what the medium. Sometimes you can break things into smaller discussion groups.
You could set up a private web forum. That's probably it for web based stuff.