Outlook and Exchange Email Issue

I have the fun task of figuring out the following:

We have Outlook and Exchange @ our office.  xyz.com domain name

Each user has their own email address:  name@xyz.com

We have an email group called sales@xyz.com that is a distrubtion group that goes to all of our sales staff.

My boss would like when the sales staff replies back to an email to:  sales@xyz.com, to reply back with the "FROM" showing sales@xyz.com, NOT the user's email address. (I know, sounds weird, but that it is my task).

I can manually select the FROM BOX in outlook, and select sales@xyz.com, but that isn't good enough.  They would like it to automatically do that, because the sales staff might forget to change the from box.  

So, if someone else bob@xyz.com, reply back using the from bob@xyz.com.  If the email is to sales@xyz.com, reply using the from:  sales@xyz.com..

Any ideas?

Thanks