Newsgroup article expiration is controlled by the configuration file /var/news/config/expire.ctl (see expire.ctl(4) for an extensive description). The file expire.ctl contains two types of entries; one for history retention, and one for newgroup article retention.
The format for newsgroup article retention is:
newsgroup:newsgroup-type:mindays:maxdays:purgerafter
For example, the entries
*:A:5:10:15 alt.binaries.pictures.animals.*:U:2:3:5
Set the default expiration parameters for all newsgroups to be "keep articles for a minimum of five days, expire articles after ten days, and purge articles after fifteen days."
Set the expiration parameters on alt.binaries.pictures.animals.*
, an unmoderated group, to be "keep articles for a minimum of two days, expire articles after three days, and purge articles after five days."
You should expire and purge articles more frequently in groups that are likely to use a lot of storage space, such as groups where binaries are posted.
After you make changes to /var/news/config/expire.ctl, you must stop then start the news server using snsnews.