Mac users - have you downloaded OS X Yosemite? How's it working for you?

[OakLeaf]

You're not wasting my time, you're giving me incentive to work harder on figuring it out for myself!

Okay, I finally imported my mailboxes, and here's what I was able to do.

Supposedly you should be able to drag the message pane closed (using the sizing bar in the top bar), but I wasn't able to do that. It would only go so narrow and then stopped. But when I switched to Classic layout (Mail>Preferences>Viewing), which has the message pane on the bottom rather than on the right, I was able to drag it completely closed (which now IIRC is the same thing I had to do when I originally set it up in Snow Leopard, it's just been so long I'd forgotten). Then once it's completely closed, it stays closed even if I switch the view back to modern layout (or whatever they call it if I un-check Classic).

With all Apple's vaunted security, it's kinda dumb to not only let it open messages by default, but make it so convoluted to turn that off ...