If you use Apple Mail in Yosemite, beware of the following issue:
A glitch in the search software in Apple’s OS X Yosemite can expose private details of Apple Mail users, revealing their IP address as well as other system details to spammers, phishers and online tracking companies.
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At the moment, the only way to work around the issue seems to be to uncheck the “Mail & Messages” box for Spotlight in System Preferences. When this option is disabled no mails are returned in Spotlight’s search results, and thus, no preview is shown.
via Glitch in OS X search can expose private details of Apple Mail users | InfoWorld.