To clear all text formatting from selected text in a composing email in Outlook, please do as follows:

1. In the composing email, select the text you will remove all formatting, and click Message > Clear all Formatting (or Clear Formatting). See screenshot:

Now you will see all formatting except the highlight color have been removed from the selected text. See screenshot:

2. Keep the text selected, and click Message > Text Highlight Color > No Color to remove all highlight colors.

So far, all text formatting including the highlight color have been removed from the selected text completely.

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