I have several different email accounts all being channeled into the same
Exchange Server mailbox for processing. The inbox is associated with a
specific email account that was created when "Sales" was created (e.g.,
sales@mydomain1.com).  When they arrive, a set of rules is run that
automatically moves them into a specific folder (e.g., if 'Amazon' is in the
subject line it is placed in an Amazon folder that I created).   All this
works great (but see next paragraph).

My problem is that when I reply to an email I'd like the reply to
automatically use what had been the recipient's original email address.  For
example, if an email was directed to johndoe@mydomain2.com and had the word
Amazon in the subject line, it would be relocated to the Amazon folder.  When
I reply to that same message, however, it shows sales@mydomain1.com as the
sender's email address instead of johndoe@mydomain2.com.

I know that the sender can manually click on the Account button and select
whatever outgoing email account s/he wants to associate with the outgoing
email message.  This approach, however, is a manual operation and prone to
human error.  Rather than trust the user to select the correct outgoing
sender's email address, I'd prefer to have a 'rule' that would do this
automatically.  I tried to create a rule for this but don't seem to find a
combination of choices that would work.  I also know that we cold ask the
user to periodically 'File|Open| Other user's folder...' and address the
problem this way (but then the operator could not size up how many unread
emails are in each of the folders).

Any suggestions?