I don't think etresoft is a troll, as he is a Level 6 here on the boards. I think that he doesn't exactly understand our issue.
etresoft, here's how the issue affects me. I hope this gives you insight into what we are discussing.
I have multiple e-mail accounts for the various aspects of my business, most POP3 accounts. In order to sync my e-mails across my different machines, I use Mail rules to move ALL e-mails I receive, regardless of the e-mail account, to the iCloud account Inbox. Thus, regardless of which machine gets the e-mail, whether it is my iMac or my Air, the e-mails go to my iCloud Inbox and are then synced between all machines.
Prior to Mountain Lion, even with all the e-mails in the iCloud Inbox, when I replied to an e-mail, the "reply-from" address and account used was the one to which the e-mail was addressed. When sent, it would use the information of that account (that account's servers) to do the send.
Here's an example to make things more clear:
I receive an e-mail addressed to pop@pop.com. Mail receives it and applies the rule that moves it to iCloud Inbox (the e-mail address of that account being icloud@me.com). When I reply, the reply-from address used, as well as all the setting for that address, was pop@pop.com. Mail sent. Done.
That's how things worked in Lion -- and in every e-mail client and operating system I've ever used. (Yes, even Windows.)
Now, in Mountain Lion, the reply-from address is changed to the iCloud account -- icloud@me.com in our example.
Try it now for yourself. Move one of your e-mails that you received addressed to a non-iCloud account to our iCloud Inbox. Reply to that e-mail. You will see that the reply-from address will be changed to your iCloud e-mail account. It shouldn't do that. There isn't an e-mail client that I know of that does that.
As I noted, this is how things worked in Lion -- and continue to work that way. I know it does as I have a machine that is still running Lion.
If it isn't obvious, this can be rather irksome to those of us who have multiple e-mail addresses. I want to reply with the correct e-mail address. I also want to keep my @me.com address somewhat private so as to separate work and play. This bug -- and it IS a bug -- makes it so that EVERY time I reply to an e-mail, I must manually change the reply-from account. Believe me, doing that a hundred times a day gets tiresome. It even gets frustrating when I forget to make that change, send the e-mail, I discover days later that the recipient didn't get the e-mail because it got caught in their spam filter because my @me.com address was not in their address book.
So that's the problem. That's the bug. I hope this helps you to understand our plight.
All the BEST!
T.