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Directly on Steemit would be a difficult since the platform is owned by Steemit Inc. The best that can be done is like to a private site where the post could be listed.

Ya, but I want my audience to be able to sort out all my posts through categorization or adding a horizontal menu.

Are our posts supposed to be lost after 7 days? They don't pay for the views after 7 days, alright, but how can audience search or discover related posts.

If you create a lot of useful posts, they must be easily discoverable, even if they are months old.

Can you suggest a solution for that on Steemit?

Are our posts supposed to be lost after 7 days?

They are not lost, they are still on you blog. But it can be hard to find if you don't know the person.

If you create a lot of useful posts, they must be easily discoverable

Search engines pick up a lot of the great posts here.