This is really odd. I only use gmail (but I don't use Google Apps). Here is the result of the four cases. I've seen this behavior for at least six months and once reported it to you, but figured I was a "one-off" and gave up on it - until today, when I saw Brian's post. I also have members complaining about "why they're getting two copies of their messages." I told one of them to uncheck the box, and she did, and reported that it did no good:
1. send message via email, "receive copies" checked: two copies of the message in my inbox
2. send message via web, "receive copies" checked: one copy, all is good
3. send message via email, "receive copies" unchecked: one copy, all is good
4. send message via web, "receive copies" unchecked: one copy, all is good.
Summary: everything is fine unless the box is checked and you send a message via email. In that case, you get duplicate copies. As Brian says, getting the two copies is really annoying. I am advising group members who experience this to uncheck the box. I don't know if there's something else I'm aware of that makes the setting necessary, since I am totally unfamiliar with the ins and outs of email. No pun intended.
Messages are the sole opinion of the author.
It's dumb to buy smart water.