I'm not a big fan of Apple's Mail. app, although I have to admit it has improved over the years and is fairly easy to use. One thing I do like about it though is the plugins you can add to it, like WideMail.
This add-on allows you to view the Mail window in full screen, just like you would in Microsoft Exchange. There's nothing too far fetched in WideMail: essentially it turns the two row horizontal view into a two column vertical view.
Some users find this appearance much easier to work with and clear.
You'll be able to adjust things like color, style and spacing of the columns from the Apple Mail preferences.
In all, it is a bit surprising that Apple did not include this possibility in the new version of Apple Mail. Having the WideMail plugin at least gives you a choice between the horizontal or vertical view.
Beware though that it can be a little unstable every now and then and can crash your Apple Mail.
Despite being a little unstable, WideMail is a useful plugin which brings vertical view to your Apple Mail.