You can moderate email for all public facing lists by enabling "moderation on public lists" on the "Email settings" tab of the "manage email lists" page.
This feature sends an email notice to all Email Admins (this is a role) about an email that has been sent to a public facing list. They must then go to the email and choose to delete it (using the link on the top left when viewing the email), or to allow it to send by editing the email and choosing to save it. This will then send a copy to the intended recipients.
Moderation is enabled for all public facing lists when this feature is check-marked.
There is no option at this time to enable it for only some lists, or lists other than public-facing.