Message moderation is what you are after, but read below.
An extract from a new HOWTO for ezmlm yet to be posted.
Common Usage/Configuration Mis-interpretations
The "Others rejected" and "User posts only" switches should be used separately (not together) as they effectively counteract each other, unless of course you want "subscribers not moderated" behaviour for your list.
The message moderation only works for posts from subscribers when these two switches (Others rejected; User posts only) are not checked, or for non-subscriber posts, if one or both the other switches are checked.
Also you may not want to use the "User post only" switch with the "Message moderation" switch. Doing so allows subscribers and "allow" people to post without moderation.
Users are encouraged to carefully read the manual and test the behaviour of their list to ensure it does what you require.
Regards
Ray Mitchell