Mail in Mountain Lion is a shambles.
Mail in Mountain Lion is a shambles. Rules do not work. If I receive a mail on one account, when I reply it defaults to my personal mac account, not the account under which the mail was received. I'm switching to Postbox until Apple sorts out Mail. The Mail client should at least be on a par with operating system - it's not; it's currently sub-standard and unusable in a professional context using multiple mail accounts.