Exchange provides a deleted item retention period. It is configured for 30 days. So generally speaking, you can recover things that have been deleted within the past 30 days.
Here's how it works. When you delete an item from your inbox, calendar or other mailbox folder, it goes into the deleted items folder in your mailbox. Normally, it will stay there until you delete it from that folder.
Here are some exceptions to that.
After you delete items from the deleted items folder, or "permanently" delete them, then the clock starts to run on the 30-day deleted item recovery period. During the 30 day period, items can normally be recovered using the deleted item recovery feature.
After the 30 day period, what's gone is gone.
Here's how to use the Recover Deleted Items feature.
When you delete something from a public folder, it does not go into anyone's deleted items folder. It is "permanently" deleted immediately.
In order to recover items from a public folder, first select the public folder which contained those items, then choose Recover Deleted Items from the Tools menu.
In order to recover an entire public folder, select the parent folder which contained it, then choose Recover Deleted Items from the Tools menu.
Here are some technical tips for how to protect your company against accidental deletion of important Exchange server data.
By choosing Exchange Hosting Service, you have taken a big step toward keeping your data safe. If you go even further and follow the steps outlined above, especially the periodic export to pst file, you will greatly reduce the likelihood of ever finding yourself in the position of having lost important data.
Thank you for your confidence, and for doing your part.