Don't receive duplicated news entries

Hello,

I'm using calibre and Kindle Touch to read news through RSS/Atom feeds and works really good. But I have one problem with this: Calibre does not detect the previously downloaded articles and, periodically, I receive feeds recipes with duplicated articles.

For example, on monday I receive the articles A, B and C, and on the next day I receive the articles B, C and D (I'm supposing that the mentioned feed only support the latest 3 articles).

Is there a way to tell calibre that ignore feeds entries existing on previously downloaded feeds?

Best Regards!