Restrict senders on Local domain only

[Samp]

HI,

Is it possible with the ZCS 6.0.3 to restrict some accounts to send mails only on local domain and not outside, or for some defined domains ?

I know it's possible with Postfix and the smtpd_restriction_classes mechanism but I can't give the possibility to mails administrators to connect to the SSH console and modify by hand the postfix conf.

Thanks in advance for your help.

Sam.