You look at your inbox on your iPhone and iPad and find it empty. You know you had messages! They’re not in your Trash or Junk folders. Where did they go? Focus on the lower-left corner of the Mail app’s view, and you’ll see a blue circle with three lines, from largest to smallest, top to bottom. That’s the Filter button, and you tapped it without realizing it. Tap it again, the blue inverts to white, and your email
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