If you are a moderator, you can use the gnus-mdrtn.el package. It is not included in the standard Gnus package. Write a mail to ‘firstname.lastname@example.org’ and state what group you moderate, and you'll get a copy.
The moderation package is implemented as a minor mode for summary buffers. Put
(add-hook 'gnus-summary-mode-hook 'gnus-moderate)
in your ~/.gnus.el file.
If you are the moderator of ‘rec.zoofle’, this is how it's supposed to work:
To use moderation mode in these two groups, say:
(setq gnus-moderated-list "^nnml:rec.zoofle$\\|^rec.zoofle$")