I did this simple hack on a private WordPress Multisite blog, to stop it
sending me emails every time I created a new blog. It’s definitely overkill
to stop all emails, but unfortunately I couldn’t find any hooks that let me
be more specific! (I didn’t need any of the other emails – but you shouldn’t
use this code if you do!)
I put the code in wp-config.php. You could create a plugin instead, or
putting it in your theme’s functions.php might work (I haven’t tested it).
// Disable ALL emails
// Do nothing!