I've pushed a new feature available to premium/enterprise groups. If you have one of those groups, in the Group Settings page there's a new Repost Policies section. You can allow members to repost messages. You can define how many times they can repost a message and how long they have to wait before reposting. To repost a message, go into the More menu when viewing the message and look for the Repost Message link. Reposted messages are tagged with the '#repost' hashtag. The feature is turned off by default.
This does not apply to someone who just emails the exact same message to the group more than once. I can extend it for that, but it could be a bit tricky. This feature was requested by a couple of groups who have classifieds subgroups where people end up reposting until something is sold.
Please let me know if you have any questions or suggestions.
