My company uses outlook for our email, and we also utilize a web-based software named CentralDesktop to manage some of our client files and tasking needs,  When users send notifications to lists of people through CentralDesktop, the notifications come into our emails and look like:

"John Smith via Central Desktop".  This saves to the list of contacts automatically.

The problem we run into, is that if you are looking to send emails to that user (John Smith) in the future, there are now 2 records available for him in Outlook.  His regular *** Email address is removed for privacy *** (which displays as "John Smith"), and then also the "John Smith via Central Desktop" address.

The issue we run into is that the 2nd email address I mentioned above is actually a distribution list, which includes ALL users who John Smith originally emailed from Central Desktop.  I'm sure you can imagine the issues this could cause when someone sends company-wide emails from Central Desktop (We use this feature very often), and then someone else tries to email ONLY john smith, and instead is sending to the entire company.

My question is, is there a way to prevent only certain email addresses from being add to the list of available addresses for Outlook Auto-complete?  

The 2 other options (albeit terrible options) I've come up with are to have users regularly delete these Central Desktop email addresses manually from the auto-complete list, or to fully disable the auto-complete feature.