You can view all unread email across all mail accounts when viewing Mailboxes in mail.app

You can also set up additional views/mailboxes for messages which match:

• To or CC
• Attachments
• All Drafts
• All Sent
• All Trash

Just tap EDIT on top left when in Mailboxes view and select the option you want displayed and where you want it located in the list.

/via http://targuman.org/blog/2013/03/20/view-unread-mail-in-ios-using-notifications-workaround/