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The part of an email that precedes the body or text of the message. A message’s full header includes detailed information about the mail servers and protocols used to route the message. Most email apps, including Mail, show an abbreviated version—typically, sender, recipients, date, and subject.
In Mail, when you move the pointer around the header area of a message you receive, buttons are shown for working with the message.
When you send messages, you can add fields to the header area, such as a Priority field, by clicking the Header Fields button .
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