Brian Vogel <britechguy@...>
What is usual/customary varies by context.
It has never, in my very wide experience, been possible to choose who one is writing to in the way one chooses who one is composing an e-mail message to in the context of a web forum. Regardless of the fact that Groups.io is a hybrid platform, people can an do have expectations that the web forum side will behave as a conventional web forum does and the e-mail side will behave as a conventional e-mailing list does. Attempts to hybridize these two are not well advised because there is such a long history of "what's conventional" in each.
PM-ing is, absolutely, distinct from reply and it always means that one has chosen who one is sending a private message to via the mechanism to do so itself. Most often this is using a click-through link to a person's profile, where a PM link/button exists, or sometimes things are set up such that the userid shown on posts will serve as its own PM trigger (this is a relatively rare exception).
A reply button on a web forum means, and only means, reply to the forum itself. It has never meant "reply to the sender" and I can't find another forum that supports this. Messages to sender are always done via Private Message, though exactly how that private message is conveyed to the recipient can vary between in-site messaging systems, e-mail, or e-mail notifying the recipient that a private message exists on an in-site messaging system.
These conventions have been in place for decades now. They are not new. Anyone who's been using either a web forum or an e-mail list knows them with regard to the environment in question. Anyone who is a newbie really needs to learn them as a part of their education process.
There is zero need to reinvent anything here.
A lot of what appears to be progress is just so much technological rococo. ~ Bill Gray