How to inspect/access config values specified in config/email.php?

I'm following the directions here which describe how to configure one's email preferences in a configuration file rather than having to call the initialize method of the Email class. I'm wondering how I might access these configuration values in the email.php file from within a controller?

The reason I ask is because I'd like to add some additional configuration values like a default_from address, some kind of server identifier so that I know whether incoming emails are from production vs. dev, etc.

Can someone tell me how to access email-related configuration values inside a controller?