Missing e-mail

[koder]

I was working in Evolution composing and e-mail. I changed my mind and
canceled it. I flipped to another desktop to browse. When I came back my
Inbox was empty. Inbox was  not listed in the folder lost on the left
pane until after I closed Evolution and restarted it. Other e-mail
folders still have their content. The
folder /home/koder/.evolution/mail/local has a file Inbox with zero
bytes that says it was last accessed today. 

It looks like the whole Inbox folder was trashed and the folder was
rebuilt on restart. Is this common? Should I be doing some kind of daily
backup of the files?

Harold