What referrer hostname do gmail.com, outlook.com, hotmail.com pass?

When someone arrives on my site, I want to check whether they came from Gmail, Outlook.com or Hotmail.com. I installed Fiddler, but I can't find a the referrer hostname anywhere when I come from Gmail. Is a referrer hostname even passed for these mail clients?

Solution

Browsers don't pass the URL in the Referer field if it is an https:// URL, because it might contain private information. From RFC 2616 section 15.1.3:

Clients SHOULD NOT include a Referer header field in a (non-secure) HTTP request if the referring page was transferred with a secure protocol.

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