Information
You can use this setting to specify how long deleted messages are retained before they are permanently removed from the database. Defining a reasonable retention period facilitates recovering accidentally deleted messages while controlling the volume of storage that retained messages require.
Rationale:
Users may want to recover accidentally deleted messages, or administrators may need to recover deliberately deleted messages for legal or managerial reasons.
Solution
To implement the recommended state, execute the following PowerShell cmdlet:
Set-MailboxDatabase -Identity MDB2 -DeletedItemRetention 14