This afternoon, my Evolution email client started popping up an error message "Summary and folder mismatch, even after a sync" as I would enter the various folders. I finally figured out a fix and everything is back to normal. If you ever get this error, the following steps solved my problem. First, close Evolution. Then run the following:

$ cd ~/.evolution/mail
$ cp -r local local.BAK
$ cd local
$ rm Inbox.ibex.index Inbox.ibex.index.data

Now reopen Evolution and you should be good. I imagine it's safe to delete the .BAK file, but I am holding onto it for a day or so. :)