I was working with one of my customer where he had applied a RPT almost 5 months ago with below conditions:
Important: No PT was applied in any folders.
RPT was not deleting mails from deleted item folder regardless we could see mails older than 180 days.
This is a by design behavior. The calculation of time stamp of RPT for deleted item folder starts the moment you have apply the policy on a mailbox. The moment you apply the policy it will start stamping items with starts and expiration date. For an example: If My deleted item has items older than 18 days and I apply RPT on 27th March 2014, RPT will stamp that item with start date: 27th March 2014 and expiration date 27th September 2014.
However, if you have an item which was already stamped with expiration date, it is expected to expire in the same date it stamped with. Unless you make changes in the policy or move the item to another customized folder where another RPT has been applied. If the customized folder does not have any RPT applied item will expire in the same date. For an example: You have an item in deleted item folder which has an expiration date stapled on 27th July 2014. Now you move that item to a new folder where RPT is not applied than the item is expected to delete in the same stapled date which is 27th July 2014. However, if you move that item to another folder where you have applied another RPT with another action then the RPT applied on the customized folder will take precedence.
Can we do anything?
Yes, we can change age/duration for the RPT which is applied on the deleted item folder. After changing age/duration we can test with one user by starting manage folder assistance and we can verify new time stamp for expiration. It will take some time to get effective. However you can Increase diagnostic for MS Exchange Mailbox Assistant -> service and Email LifeCycle Assistant to Expert. It will help you to trace the chance in the app log.
If you wait for some time you will see the new change will be applied in the items and items will process after that.
Important: It will stamp new time for all messages and after that it will perform requested/configured action.
Caution: Applying Retention policy tag during business hours may cause performance issue as it requires Exchange resources. Therefore, you are requested to perform any RPT changes during off business hours to avoid performance issue.