From: Yahoo! [firstname.lastname@example.org]
Date: 14 June 2013 08:42
Subject: We want you back
Signed by: email.yahoo-inc.com
We want you back.
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It just looks so much like a phishing email that a sensible person probably wouldn't click on it.. except, the links in the email actually go to Yahoo! and the email has been signed, so this really does appear to be a genuine email.
Except for one thing.. the email address that it was sent to has never been used to register a Yahoo! account. Yup.. something somewhere is not right with this email..
Yahoo!'s explanation can be found here.