restrict user to send mail to particular email address only

Dear Sir,

I want to do setting in zimbra 7.1.3 open source edition. restrict user to send mail to perticular email address.

example:- abc@xyz.com should not sent mail to abc@gmail.com ID only.
he can sent mail to other gmail IDs.

How can I accomplish this task?

please help me.

Thanks,
shashikant sutar