Thanks for those points, we're trying hard to succinctly explain what we do.

We start by saying it's not email because it's easy to think plum mail is yet another email client, which it isn't.

plum mail hosts the conversations so it can manage the state of pinning, conclusions etc.

email addresses are just a user identifier it will email people if they are not on plum mail, so we don't require someone to be on plum mail for you to start talking to them.