Composing messages in Apple Mail: Displaying text on screen in larger size without changing font size When composing messages in Mail.app, as I now have an HD screen on my MBP, the default Helvetica 12pt appears quite small.  

I would like to be able to enlarge the text size, but only locally, without changing the font in the message, as I don't want the recipients to have jumbo-size text on their screen.

Is there a way to perform this kind of "zoom" without using the "Universal access" zoom features which are a little bit too much.
You can go ahead and set it to what you want in Mail Preferences.  These settings have no effect on what is seen at the other end.  To do that you have to change the font for each outgoing individually in the New Message pane.