What is not considered a “source” in Google Analytics by default?

Every referral to a web site has an origin, or source. Possible sources include: “google” (the name of a search engine), “facebook.com” (the name of a referring site), “spring_newsletter” (the name of one of your newsletters), and “direct” (users that typed your URL directly into their browser, or who had bookmarked your site). So, the three default sources are direct, referral and organic. Email is not a traffic source by default. Tip: You can use Custom Campaigns to tag links to use your own custom values for Campaign, Medium, Source, and Keyword.