My special mailboxes have vanished. How can I get them back?

they're ones I set up in order to file various material that arrives frequently, i.e., monthly newsletter, committee minutes, vacation arrangements, etc. It's material I want to be able to find quickly, but not necessarily frequently. Each mail site had its own name and they were located to the left of the column labelled "mailboxes. All of the sudden they vanished. I can find the list of boxes, but I can't access them.