I mean if a user doesn't login for ages, then the new posts count will show as 100s. Can it not do that and just show the new posts from say the last month?
Ok it was already set to 30 days. So if I login as a user and see 300 posts unread. If I wait 30 days then log back in, that will be no unread, presuming there have no new posts in that 20 day period.