In some cases, users have stated that they would like to receive notification when a specific topic is being discussed on the forums. GroupServer now tracks the keywords that describe a post and a topic, which provides one of the basic pieces of information needed for search alerts.
Somehow a user indicates that they would like to receive notification when a post or a topic is created that is tagged with a certain keyword.
Then, once a post is made, GroupServer would search for all users who have indicated that they wish to be notified of posts tagged with a keyword, and email those users a message indicating that such as been made. This email could include the the url to the post, as well as a clip of the text.
The search-and-email-on-post method described above will probably be taxing on servers. A couple of alternative implementations include:
Alert Lookup Table
Create a database table that is simply (groupId, keyword, userId). When a post is made, this table is queried for the specific groupId/keyword to retrieve all users who want to be alerted about the post. Databases are a lot more efficient at searching and retrieving, and the lookup table method is a lot more efficient than the naive search-all-users method above.
Similar to the current Topics Digests, alert emails could be generated only every X hours.