Accidentally Deleted Inboxes

I have five e-mail boxes. In addition to each box showing in my Apple Mail, they were also grouped together as "All Inboxes," "All Sent" and "All Drafts." I accidentally deleted the "All Inboxes" section. This is what I used daily to check my mail as it showed whether there was mail in each box without the need to check each box individually. As soon as I did this, I clicked on the "undo" button but it did not bring it back. Each mailbox still shows on my screen but I would like to have the inboxes grouped together as they always have been. How can I bring this back? Any help would be greatly appreciated.