Topic: Sent to internal domain only

Is it possible to configure a domain that it can only send email to domains configured on the mailserver?
We would like to create a domain that can only be used for internal communications and doesn't have an MX-record as well.

We are using iRedMail 0.8.4 LDAP Backend. with iRedAdmin-pro 1.9.0 on a CentOs 6 x64 server.

With kind regards,