In the reading area of Outlook as well as the window of an open email, the subject is visible at the very top. If you click in the subject area, you can edit it. This has several advantages. For example, you can adjust the subject directly in the mail window when replying or forwarding, or integrate important information such as customer numbers or order numbers. Since Outlook also indexes this area, you can find e-mails with effective subject lines more easily via search.