The new Async Google Analytics code (that you’re using) works a bit differently than the non-Async. Any time that you want to call a method on pageTracker you simply push a “message” onto the “_gaq” queue.
<a href="https://stackoverflow.com/questions/3503511/mailto:hello@mydomain.co.uk" onClick="_gaq.push(['_trackPageview', '/mailto/hello'])">hello@mydomain.co.uk</a>
Although, tracking a mailto link may work better as an event:
<a href="https://stackoverflow.com/questions/3503511/mailto:hello@mydomain.co.uk" onClick="_gaq.push(['_trackEvent', 'mailto', 'home'])">hello@mydomain.co.uk</a>
For more info take a look at the Async Tracking Users Guide.