If you want to include a URL link in Apple Mail, it’s easy to do, but only if you know how. Here are instructions, in 3 easy steps.
1. While you are in the message compose window of Apple Mail, choose “Customize Toolbar”, from the View menu.
2. In there, you’ll find a “Link” button. Drag this into your toolbar (the grey area in the window above the message, and then all new messages will have it there.
3. Highlight some text in your message which will be your link name, click the “Link” button now in your toolbar, enter a URL, and you’re done.
You can also use Customize Toolbar in the main message window for a bunch of different button options, e.g. colorization, that apply to that window, and you’ll find the same capability across Mac OS X.