Disable sending of any mail to certan user...?

[bulforce]

is there a way ME az administrator to disable the sending of any mail to some of the users that is under reseller account, and the reseller to be unable to re-enable the sending mails function.

[rbtux]

of course... remove the mx entries and the entries in the postfix lookup tables (don't forget the ones in (etc/ispcp/working))