Hello Tim,
What you are asking for sounds like a user|domain level IDS block list combined with a blacklist on the domain|user level as well.
I can pass this along to see if this is viable. Just on the surface this would cause a huge issue with performance. The system would need to check ever domain and user config file before even allowing the initial SMTP connection to be made.
Thank you
Tony Scholz
System/Network Administrator
SmarterTools Inc.
www.smartertools.com