How can I make Apple Mail show the URL (in mails) when I hover over a link? There is a related question for Safari but I am interested in a solution for Mail. The ⌘View menu. 

I am using OS X 10.10.5, and I would really like to see the real full link I would follow, especially with potential phishing mails.
Just hover the cursor over the link for a few seconds. The full URL will spring up underneath.

The down arrow that will also appear next to the link will open it in a Quick Look window rather than a browser - but if you want to check the link is safe first, don't use that until you're sure.