End user configurable per user whitelisting via MAIL FROM: ?

[VR]

I have Postfix running on Debian in front of Microsoft Exchange 2003 
using transport_maps, relay_domains and relay_recipient_maps. This 
Postfix configuration is purely for inbound SMTP traffic.

Is there any existing solution that enables end-users to manipulate a 
postfix "check_sender_access" type of white list, per user, that would 
also only apply per destination email address?
E.g. john...@mydomain.tld can only influence messages destined for 
john...@mydomain.tld?

I realize the editing of said lists would have to be via some other 
customized mechinism like Samba but I'm wondering if someone has been 
down this road successfully or any pointers on what the Postfix end 
might look like to achieve this?