The one feature I've long lamented not being accessible in Apple Mail - past or present - is text highlighting. It's a crux that has kept Outlook on my Mac as I use highlighting fairly regularly for work. Luckily I found a hack that you can use to bring this critical feature to Apple Mail.
First, open TextEdit and type something - anything. Then, choose the Hightlight button (in red below):
Select any color you wish to highlight with; I went with a standard yellow shade. In the application menus, choose Format > Font > Styles... and you'll be greeted with a popover window like this:
Leave the radio button option for Document Styles selected and click the Add to Favorites button. You'll get a another window asking you to name the style and the options associated. In the below screenshot, I've already named the style "Yellow Highlighting". Leave the options for include font and ruler unchecked, then click Add.
Before you proceed on, if you wish to create presets for other highlighting colors, you can do this now, otherwise you'll have to create them when you need them.
Switch back over to Apple Mail and start a new email message. When you have a section of text in the body of your email you want to highlight, select it with your cursor, and right-click to access your contextual menu options. Choose Font > Styles... and you'll be greeted with a familiar looking options window:
In the style options dropdown, select the name of the previously saved style (in this case "Yellow Highlighting") and you'll see the preview view of your text change to the parameters you previously saved. Choose Apply to update the text in the body of your email accordingly. Just like that, your email will update to show the text in the highlighted style:
Until Apple builds in a shortcut key for this exact function in the Mail app, you'll need to access the contextual menu to choose the highlighting. If you're a fan of navigating application menus, you're out of luck, since the only way to access the text style options is via right-click (at least on my Mac, the menu option is greyed out). The good news is that since the Styles menu option is standard throughout OS X, you can reuse your created highlights in other Mac apps.