Blocking email sent to specific users

[Leighton Fehr]

Hi.
I have QPopper 3.1.2 installed on my Linux RedHat 6.2 server.
I am looking for a way to block email sent to one of my users and haven't
been able to figure it out yet.  I want to block everybody, except the users
on my mail server, from being able to send messages to a particular account.
But I don't want to block access to the other accounts on my mail server.
Is this possible with QPopper?  If so, how would I find out more info on how
to do it?

Thanks for your help,
Leighton