Retention policy is not applied as expected

Hi,

I have created a retention policy on a folder of a user in exchange 2010. The policy tag is to delete contents of this folder after 15 days. After 15 days, the messages are not deleted but a note is inserted above the message saying "This item will expire in 0 days. To keep this item longer, apply a different Retention Policy."

The policy action is to delete the message permanently. But why the messages are not deleted even though it says it is expired?

Thanks for the help