mailbox column missing in mail

I get both yahoo and gmail messages in my Apple Mail (version 7.3) in Mavericks 10.9.5 Had not problems until the last few days (well, minimal). I like have "mailbox" in the column headings so I can see at a glance where the message is coming from. But for some reason, it keeps disappearing. I keep checking under View - Columns - Mailbox and it is fine until I close the viewer. When I reopen, it is gone and I have to reselect it.

Any fixes?