Admin page Dashboard > Settings > Discussions
These settings provide you even more control over the instances of when and how comments are posted.
An administrator must always approve the comment
Select this option to force comments to be approved by a blog user or owner having the proper Role to approve comments, even if the comments appear to be spam. See the Comment Moderation options below regarding spam.
Comment author must have a previously approved comment
Check the box to insure comments are only posted if the comment author’s email address matches the address of a previously approved comment, otherwise, the comment is held for moderation. Comments from blacklisted email addresses (those listed in the Local Spam Words Text Box) are held for moderation regardless of white-list status.