I know we all know Google is evil, but my solution to this problem has been to use GMail (and Google's official GMail app for iOS). You can create a GMail account and set up all your other accounts (home, work, etc) so they'll forward every new e-mail message to your GMail account the moment it arrives (you can also tell them to delete the original messages when they forward them to your GMail account, so your inboxes will never fill up). You can then set your GMail account up so that, by default, when you click "reply" (or "reply to all" or "forward") the reply will be sent from the e-mail address the original e-mail message was sent to (this will also work on the iOS GMail app, but I believe you must set it up from an actual computer). Finally, you can create filters and labels so you'll automatically know which "inbox" the message you received sits in (home, work, etc).
Not exactly what you expected, but maybe it will help.
Cheers!