You may not be able to. An email does not need to be associated with a website. Also, just because a site is not fake does not mean that emails purporting to relate to the site are legit. Without seeing the email its impossible to provide informed comment.
That said, the first step in tracing the email is to access "Full Headers" for it, and then look at the delivery chain - paying most attention to who delivered it to your mail provider. It is then a matter of working back through that chain with the support of the senders email provider - in the unlikely event you can get it.
Depending totally on the email there are some things you may be able to do to short-circuit this process, but without the email, one can't even start to tackle that problem.
1How is the "windows-7" tag relevant? Emails and websites are not mutually exclusive. – David Custer – 2015-07-03T05:24:38.957
check email headers in your email,if the website was bothering why not unsubscribe it?it doesnt suite this site,kindly ask at security.stackexchange – BlueBerry - Vignesh4303 – 2015-07-03T05:28:51.773
What do you hope to achieve once you find out where the email is being sent from? – Ramhound – 2015-07-03T05:33:39.327