Actually, I had an issue with Mail when I first started. In years past, after an OS X upgrade, Mail.app would show a "Upgrade Mail" prompt before using. Now it

Actually, I had an issue with Mail when I first started. In years past, after an OS X upgrade, Mail.app would show a "Upgrade Mail" prompt before using. Now it appears that instead, it's happily showing a blank set of emails while it slowly (5 minutes-ish for me) converts to the new version. This is, of course, confusing to the user because it doesn't show ANY indication that it's converting to a new version. So likely, it's still converting the emails. That's why CPU spikes when you first load too; it's not Spotlight but the conversion process (and Spotlight is reading them while converting).