An item that is often asked about is does the Recover Deleted Items folder contribute to the users mailbox quota? The answer is No. Microsoft has documented this on TechNet under a bazaar location.
Items in the Recoverable Items folder aren't calculated toward the user's mailbox quota. In Exchange 2010, the Recoverable Items folder has its own quota. When a user's Recoverable Items folder exceeds the warning quota for recoverable items (as specified by the RecoverableItemsWarningQuota parameter), an event is logged in the Application event log of the Mailbox server. When the folder exceeds the quota for recoverable items (as specified by the RecoverableItemsQuota parameter), users won't be able to empty the Deleted Items folder or permanently delete mailbox items. Also copy-on-write won't be able to create copies of modified items. Therefore, it's critical that you monitor the Recoverable Items quotas for mailbox users placed on litigation hold.
For mailbox databases, the default RecoverableItemsWarningQuota and RecoverableItemsQuota values are set to 20 Gb and 30 Gb respectively. These settings are usually sufficient for storing several years of mailbox data when on litigation hold. To modify these values for a mailbox database, use the Set-MailboxDatabase cmdlet. To modify them for individual mailboxes, use the Set-Mailbox cmdlet.