When looking through your inbox in the Mail app on iPhone or iPad, you can see a preview of the contents of the message. This presentation may be more useful than display a single line for incoming mail.
But you may wish certain users to control the number of lines of the message content that will be previewed in the message list for each message. Follow the steps here below to learn how to change the number of lines in the preview.
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How to change the preview list of messages in the Mail app on iOS
1) open your settings and select Mail.
2) in the message list Message List, click the preview of the Preview.
3) Choose the number of lines to display, from “none” to “5 Lines”.
4) Click on the arrow at the top to return to your mail settings number or close the app.