Comment Probation allows you to put a comment author on “probation.”

If you allow comments to automatically appear from authors who already have an approved comment,
this plugin gives you a bit more control. It lets you approve a comment but place the author
under probation, meaning that any future comments from that author will need to be moderated again.

When approving a comment, you’re given the option to “Approve” the comment, or “Approve with Probation.”
If a comment ended up in moderation because the author is on probation, “approving” the comment will
remove the author from the probation list.