How can I disable Mail.app when I click on an email address?
Notwithstanding any sneaky Terminal commands I know not about, OS X will always have the need to open some app upon clicking an e-mail link. Literally any app of your liking will do.

Such an app might be an app you don't mind being opened. Like… the Finder!


Open Mail Preferences and go to the first tab, General. Choose the pop-up menu for Default email reader and pick Select….


Choose Macintosh HD (or whatever you've renamed your boot volume to) → System → Library → CoreServices → Finder.app.


Try it out! (I can't post mailto: links here though. )


If you work with spaces or full-screen apps, clicking a mail link might switch spaces. But at least no apps are launched. On my computer, not even a new Finder window is opened.