We mentioned improvements to Spotlight earlier and Safari is adding some of those same sources within its smart-search field. In addition, you'll have the option to choose DuckDuckGo as the default search engine. (Among other things, DuckDuckGo provides greater privacy than some other search engines.)
Yosemite's Safari additionally offers an advanced Private Browsing mode (in which your browsing actions aren't tracked or saved). With today's Safari, when you switch on Private Browsing it applies to all open Safari windows. With the next version of Safari, you'll be able to create a window and devote it — and all the tabs within it — to private browsing. As with Safari on iOS devices, the color of the browser window will change to help you identify private windows. You'll be able to maintain separate windows that aren't configured to be private.
Has Apple removed the 'Reader' feature in Safari?
No! Reader and Reading List are still alive and well in the OS X Yosemite version of Safari; they've just been simplified. The Reader icon is now to the left of the search field, and is presented as a series of horizontal lines. Hover over that field, and you'll see a plus button to the right of the Reader icon; clicking that will send the webpage in question to your Reading List.
Any changes to the Safari sidebar Apple added in Mavericks?
Nothing major: the sidebar still houses Shared Links (links posted by people you follow on social networks), Reading List items, and bookmarks. A big upgrade to Shared Links is the ability to subscribe to individual websites — this is actually the return of RSS feeds to Safari. When you visit a site, if you click the Share button (in the upper right corner of a Safari window), on many sites you'll see a new Subscribe in Shared Links option. This essentially adds the contents of that site's RSS feed to your Shared Links list. For hard-core RSS users, this will probably not be useful. But more casual users might find Shared Links to be a good place to find new items to read, including items from favorite sites. We'll see.
What's new in Mail?
The two major new features are Markup and Mail Drop. If you've had occasion to annotate images in Preview, you'll get the gist of the way Markup works: When you add an image to an email message, you'll be able to invoke annotation tools to mark it up. These tools are remarkably similar to those you find in Preview: you'll be able to add shapes, arrows, and text and to fill out and sign PDF documents either by drawing in your signature or using one you've captured with a webcam.
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