Emails which got deleted from the outlook are first saved in the Deleted items and further deletion will move it to the Recover Deleted Items folder. What happens after that?
1. If you have your complete infra on Office365, the restore is not possible. Deleted is deleted.
2. If you have Hybrid setup but no Retention policy and Online Archival Setup, Cannot restore.
3. If you have Hybrid setup with Retention policy and Online Archival setup, then the restore is possible.
Here is the flow of emails which are getting deleted.
Outlook Client -> Outlook Deleted items ->Outlook Recover Deleted Items -> Discovery Server.
How to retrieve the emails from the Discovery Server?
Open OWA -> Options > Manage your Organization > Roles > Grant yourself “Discovery Management Role” > Wait for the replication.
After approx 20 mins > Goto Mail Control & you can see a new Tab > Discovery.
Click Discovery > Click New > There are options to search for Keyword or complete Mailbox.
After choosing complete Mailbox > The Estimation will be done first and then the Search will be done.This will display the size of the mailbox retrieved.
Now, we need to merge this result to the Discovery Mailbox. Click on the Search and click Details > Click “Search Name, Type and Storage Location” and choose the option button “Copy the search result to destination Mailbox” and the discovery Mailbox is chosen by default. Click Save.
Allow some time replication, connect the Discovery Mailbox on your outlook and traverse to the location of the searched Mailbox to fetch the result.