How so? I email two to four people very frequently. That is much easier than creating a mailing list for every possible combination of PM, Tester, and Doc Writer who works on any feature with me.
Because that only makes sense if you want them replying to everybody else, which is almost never the case, or you'd just make a real mailing list. I'm not saying "don't send e-mails to multiple people" I'm just saying "use CC appropriately."
I, for one, would be safe using e-mail this way: none of my relatives even know where the "Reply" button is (though they long ago located Forward, sadly.) They just create a new message addressed to the original sender when they have something to say.
