Block Specific Email to Specific User

[fuzzie]

OK, weird question time.
I need to block a specific email from a specific user so that the email address can't be delivered to that user. Now for the complicated part. I need to make sure that email gets a bounced message.
I can do it domain-wide, but only a fail which seems to go to NULL. I need to restrict it to just a single user, and it has to bounce.

Any idea how I do that?
Thanks so much!

[lloyd_tennison]

I had this to block a sender (ages ago)- but can probably modify to a receiver:


deny message = Quit Bothering Us. Get a life.
log_message = John Doe - Go Away and Quit Bugging Us
senders = s123@yahoo.com
condition = ${if match {$sender_fullhost}{\Ns123@yahoo.com$\N}{no}{yes}}