When you initially import your OPML file or add a new subscription, we just mark the latest 10 posts in your subscriptions as unread. However, all new posts
will be added to your unread items as they get published.
For free users, we keep the last 2 months of unread posts, up to 300 posts per feed. So, if there's a feed that is particularly busy and posts more than 300 times in the last 2 months, we will cleanup those posts that are over the limit 300, no matter how old they are.
For premium accounts, we keep the last 1 year of unread posts, up to 1000 posts per feed.
If a free user and a paid user are subscribed to the same feed, then the free user will still have the 2 month unread limit, but up to 1000 posts per feed during that 2 months.
It is important to note that posts are kept up to the feed limit (300 for free, 1000 for premium), and are visible as unread items and available to search to all users who are subscribed to those feeds. The 2 month/1 year restriction only applies to unread items.
Shared, commented, or liked posts are stored forever for both free and paid users.