Never mistake live site for the test site

Ever made a change during development or testing content on a website, believing you are just testing you local site but in fact you just changed the live site instead? Or vice versa.
With this plugin you get used to the red rectangle with the lettering Local site and the [LOCAL] prefix in the title bar.

It could be a bit more clear that the emails are only redirected when the WP_LOCAL_EMAIL variable is set:

define( 'WP_LOCAL_EMAIL', 'me@example.com' );